
## Your Bikepacking Power Budget in Watt-Hours, Start to Finish

Build a bikepacking power budget in watt-hours like this. List every device. Convert each battery with `Wh = mAh / 1000 × V`. Estimate the fraction you spend per day, sum those, then divide by the share of a power bank's label you actually receive. The rule we derive below: **rated mAh is roughly 400 times your watt-hours per day times your days off-grid.**

The uncomfortable part first: the number printed on the side of a power bank is not the number you get. It describes energy in the cells at about 3.7 V, not energy leaving the USB port at 5 V, and the conversion takes a cut. Riders who size a bank off the label run out on day three and conclude the bank was faulty.

One conversion, one table, one division. It is the step that makes every other decision about [how a bikepacking charging system fits together](/posts/bikepacking-power-charging-guide) answerable with a number instead of a hunch.

<Highlight label="The short version">

- **One conversion only.** `Wh = mAh / 1000 × V`. A device cell quoted at 3.7 V and a USB port delivering 5 V are not the same currency.
- **Count watt-hours per day, not devices.** A phone navigating with the screen on is worth roughly ten satellite messengers.
- **Assume about 70 percent of a bank's printed energy reaches a battery.** Anker's own support pages put the boost circuit at about 82 percent and the receiving device at a further 15 percent loss.
- **Size for every day of the trip.** The credit for leaving the last socket full cancels almost exactly against the day of reserve you should carry.
- **The shortcut:** rated mAh is about 400 times watt-hours per day times days between sockets. An 18 Wh-per-day rider going five days needs roughly 36,000 mAh of label.
- **Check the 100 Wh line before you fly.** That 36,000 mAh works out at about 133 Wh, over the FAA's 100 Wh threshold for carry-on without airline approval — and individual carriers can be stricter.

</Highlight>

<SectionDivider variant="trail" />

## The One Conversion You Need: mAh to Watt-Hours

Milliamp-hours measure charge, not energy; charge becomes energy only when you multiply by a voltage. That is the whole trap — two batteries with the same mAh figure can hold very different amounts of electricity. The conversion is `Wh = mAh / 1000 × V`, and backwards, `mAh = Wh / V × 1000`.

Work one through. Apple leaves capacity out of its standard tech specs, but EU energy-label disclosures include it, and as reported by Notebookcheck those put the eSIM iPhone 17 Pro at 4,252 mAh. Macworld's comparison table converts that to 16.56 Wh — and lists the physical-SIM variant lower, at 3,988 mAh and 15.53 Wh, so check which version you own. Note that 16.56 divided by 4.252 implies a nominal voltage near 3.9 V, above the 3.7 V most capacity guides assume — the two conventions disagree by a few percent. We use published watt-hour figures where they exist and the 3.7 V convention where they do not.

Now the same arithmetic on a power bank. Anker's support pages work it explicitly: a 10,000 mAh bank holds about 37 Wh at 3.7 V, which at 5 V is only 7,400 mAh, and after roughly 82 percent circuit efficiency about 6,068 mAh. That is why banks advertising 10,000 mAh often carry a second, smaller rated figure near 6,000 mAh elsewhere on the label.

<PullQuote>A power bank's headline number is a statement about its cells. It is not a promise about your phone.</PullQuote>

## What Your Devices Actually Draw Per Day

The awkward reality of bikepacking electronics is that the devices you worry about are rarely the ones emptying your battery. A head unit recording a track is a small, steady load. A phone used for live navigation with the screen lit is the largest line in most budgets, by a wide margin.

Makers also publish inconsistent things: phone capacities in mAh because of EU labelling, head units and messengers as claimed runtime with no cell capacity at all, lights somewhere between.

| Device class | Published figure we could find | Realistic daily use | Watt-hours per day |
|---|---|---|---|
| Phone, live navigation, screen on | iPhone 17 Pro, eSIM, at 4,252 mAh per Apple's EU energy label, 16.56 Wh per Macworld | 60 percent of the battery | about 10 |
| Phone, offline maps, screen mostly off | the same 16.56 Wh | 25 percent of the battery | about 4 |
| Head unit recording all day | Wahoo claims up to 20 hours for the Elemnt Bolt 3; no cell capacity published | 7 hours, about a third of a charge | about 3.5, assuming 10 Wh per charge |
| Satellite messenger, 10-minute tracking | Garmin's inReach Mini 2 specification: up to 14 days at 10-minute tracking with a full sky view | one charge per week | under 1, assuming 5 Wh per charge |
| Front light, one hour at a mid setting | Lezyne Macro Drive 1400+ listed at 5,200 mAh and about 3 hours in 1400-lumen Overdrive | 1 hour, well below full output | about 3 |

Two of those rows contain an assumption rather than a specification, and we would rather flag it than hide it. **Neither Wahoo nor Garmin publishes a cell capacity for its head units** — Garmin lists the Edge 1050 at up to 20 hours in demanding use and up to 60 hours in battery-saver mode, which tells you hours and nothing about watt-hours. The 10 Wh per charge above is our estimate and the softest number in this article. Claimed runtimes are not a ceiling either: Cyclists Hub measured about 26.7 hours from a Bolt 3 against the 20-hour claim, and the5krunner roughly 25 hours with the backlight off. Our [cycling computer roundup](/posts/best-cycling-computers-bikepacking) collects the claimed figures across the field.

The light row is firmer because the capacity is published. A 5,200 mAh cell is about 19 Wh at 3.7 V, so if the listing gives roughly 3 hours at 1400 lumens, full output costs about 6.4 W. You will not ride on full output, and the same listing gives 950 lumens for 4 hours and 450 lumens for 12.5 hours — about 4.8 W and 1.5 W off that 19 Wh cell. That is why the hour at a usable setting in the table costs around 3 Wh rather than six. Bike Perfect's review of that light notes the quoted run times are optimistic — our guide to [lights for overnight bikepacking](/posts/best-bike-lights-overnight-bikepacking) goes through the modes that matter.

Sum the nav-heavy rider: 10 plus 3.5 plus 1 plus 3 is 17.5 Wh. **Call it 18 Wh a day.** Swap live navigation for offline maps and the same rider drops to about 11.5 Wh — a 36 percent cut from one behaviour change, worth more than any purchase. Our look at [bikepacking navigation apps](/posts/best-bikepacking-navigation-apps) covers which ones make it cheap.

<SectionDivider variant="rule" />

## Usable Versus Rated Capacity: Sizing a Power Bank for Bikepacking

Sizing a power bank for bikepacking means working backwards from watt-hours into cells, and paying two taxes on the way. The first is the boost circuit: cells sit near 3.7 V and USB needs 5 V, so something steps the voltage up, and Anker's support material puts that conversion at roughly 80 to 85 percent efficient, the rest lost as heat and to internal resistance. The second is your own device, which loses roughly a further 15 percent while charging, per the same source.

Multiply those and about 70 percent of the printed energy ends up in a battery. Anker's worked example for a 20,000 mAh bank is 74 Wh at the cell and about 60.7 Wh after conversion — and once the receiving device takes its share, something near 52 Wh of stored charge.

These are a vendor's own figures, not independent lab measurements, and Anker notes real efficiency varies by device. Treat 70 percent as a planning number rather than a constant; for a cold or cheap bank it is probably optimistic.

<Warning title="Sizing off the label is the classic error">

A rider who needs 90 Wh of delivered energy and buys a 20,000 mAh bank because "74 watt-hours is plenty" is about 38 Wh short — more than two days of budget. The bank is not faulty; it was never going to deliver its label, and nothing on the packaging says so. Convert to watt-hours, then divide by 0.7.

</Warning>

## The Worked Example: How Much Battery Capacity for a Week of Bikepacking

Here is the method on one rider — a worked example built from the published figures above, not a trip report. We have not metered these devices.

**The assumptions.** Seven-day gravel tour. Phone used for live navigation, head unit recording about 7 hours a day, satellite messenger tracking at 10-minute intervals, an hour of light most mornings. Daily total 18 Wh. The longest stretch without a wall socket is five days.

**The sum.** Five days at 18 Wh is 90 Wh that has to reach a cell. Two corrections apply, pulling opposite ways. You leave the last socket with every device full, worth roughly a day — true here, because each device holds at least one day of its own consumption. Then you add a day of reserve, worth the same.

<PullQuote>Subtract the day your devices start full, add a day of reserve, and the two cancel. Size the bank as if it must carry every day of the trip.</PullQuote>

**The conversion.** 90 Wh into cells, divided by 0.7, is about 129 Wh of printed capacity. At 3.7 V that is roughly 35,000 mAh. The shortcut — 400 times watt-hours per day times days off-grid — gives 18 times 5 times 400, or 36,000 mAh. Same answer.

**Therefore:** about 35,000 to 40,000 mAh of rated capacity, which in practice means two 20,000 mAh banks rather than one enormous one. That split is not only about redundancy. A 36,000 mAh bank is about 133 Wh, and the FAA's own PackSafe guidance puts the limit for carry-on without advance airline approval at 100 Wh per battery, with 101 to 160 Wh needing airline approval and a cap of two spare batteries. The FAA also notes airlines may set limits stricter than the federal baseline, so check your carrier before you book. Two 74 Wh banks each clear the line. One 133 Wh brick does not.

That total is also the moment to ask whether you should carry the energy at all. Thirty-five thousand mAh of lithium is a real weight penalty for five days of autonomy, and this is the crossover where [choosing between a dynamo hub and a power bank](/posts/dynamo-hub-vs-power-bank-bikepacking) stops being theoretical. Below three or four days off-grid the bank wins easily; above it, generating looks cheap. Once you have the number, our guide to [picking a portable charger for your phone and GPS](/posts/navigating-with-power-the-best-portable-charger-for-your-phone-and-gps) covers which bank to buy.

**The weekend pass.** Same rider, two days without a socket. 18 times 2 times 400 is 14,400 mAh, rounding up to a 20,000 mAh bank. But the formula over-buys on short trips, because the day your devices start full is half of a two-day window instead of a fifth of a five-day one. A 10,000 mAh bank delivers about 26 Wh into cells against 18 Wh of real need, covering the weekend with half a day spare. We would take the 10,000 and accept the thinner margin — and on offline maps at 11.5 Wh a day, it becomes genuinely comfortable.

<SectionDivider variant="ornamental" />

## The Reserve, and What Eats Your Budget Without Warning

Three things reliably spend power you never budgeted.

**Cold.** Capacity falls as temperature does, and the published numbers are chemistry-specific. A 2025 study in *Batteries* of a commercial LiFePO4 module measured capacity down about 15 percent near -10 °C and about 35 percent near -20 °C relative to room temperature. That is a different chemistry from the pouch cells in your phone, so read it as a direction rather than a figure for your kit. Battery University's own page on discharging at high and low temperatures is consistent in shape: cold temperature increases internal resistance and lowers capacity, and that reduced capacity applies only while the cell is cold. Battery University does not prescribe a bigger pack for cold riding — sizing up is our inference from the loss figures, not its advice. Our [cold-weather bikepacking guide](/posts/winter-bikepacking-cold-weather-guide) covers keeping a bank warm, which is cheaper than carrying a bigger one.

**Losses you pay twice.** Topping a power bank up from a dynamo and then charging a phone from the bank pays the conversion tax twice, so the delivered figure is lower than a single-stage estimate suggests.

**A device hunting for signal.** The same Garmin specification that gives 14 days of 10-minute tracking with a full sky view gives about 4 days under moderate tree cover, which is the default setting — a cut of more than two-thirds from sky view alone, with no change in how you used the device.

<Tip title="The reserve rule we use">

Carry one extra day of your daily watt-hour figure and never spend it on navigation. The reserve is for the detour, the unplanned bivvy and the hour spent with the phone out working out where the track went. If you ride in the cold, make it a day and a half. Our separate articles on [charging your devices on route](/posts/charging-devices-on-route-bikepacking) and device power management on tour cover recovering a budget that has already gone wrong.

</Tip>

## Check Your Real Consumption on a Shakedown Ride

The table above is a starting point, and the head-unit row is an estimate. Replace it with your own numbers on a ride you can bail out of. Charge everything to full, ride a normal day with your real settings, and write down the percentage left on each device that evening. Percentages are enough: 40 percent of a 16.56 Wh phone battery is 6.6 Wh, and that is a measurement rather than a guess.

Then test the bank. Run a full power bank down charging your actual kit and count the device-charges before it dies. That figure is your real usable capacity, and it either validates or demolishes the 70 percent assumption.

Change one thing at a time afterwards — recording interval, backlight, screen timeout and radio settings all move the number, and three changes at once tell you nothing.

<SectionDivider variant="trail" />

## What To Do Next

List your devices tonight. Convert each to watt-hours with `Wh = mAh / 1000 × V`, using published figures where you can find them and flagging your estimates. Sum your daily total, multiply by 400 and by your days between sockets, and you have a rated capacity to shop against.

Then take the tradeoff seriously. The arithmetic usually says carry more lithium than you expected, and the honest alternative is to need less electricity — offline maps, a dimmer screen, a longer recording interval. We would do that work first and buy the smaller bank second. To turn the number into a system, start with [the full bikepacking power and charging guide](/posts/bikepacking-power-charging-guide).


How Much Battery Do You Actually Need? Bikepacking Power Budgeting

Bikepacking Power and Charging: The Complete Guide to Staying Charged Off-Grid


## Where to Charge Devices While Bikepacking: The Short Answer

Cafes, public libraries, laundromats, campground shower and laundry blocks, grocery stores with seating, visitor centres, transit stations, hostels and bike shops. On a populated route you are rarely more than a day or two from one of them. **The skill is not finding sockets. It is recognising them, and arriving able to use the forty minutes you actually get.**

A rider with a dynamo makes power while pedalling. A rider without one buys it in short, scheduled bursts, and the system lives or dies on how much a single stop can swallow. Bank size, cable choice and charge order in [bikepacking power and charging](/posts/bikepacking-power-charging-guide) are all downstream of that constraint.

<Highlight label="The short version">

- **Sockets cluster where people sit.** Food, laundry, books, showers, waiting rooms. Outdoor ones are unreliable, often dead at a breaker you cannot see.
- **Charge the big thing from the wall.** The power bank takes the socket. Your devices feed off the bank later, while you ride.
- **Forty minutes at 20 W is about 13 Wh** before conversion losses, or roughly a third of a 10,000 mAh bank. Forty minutes from an old 5 W brick is about 3 Wh, which is close to nothing.
- **The charger and the cable set the ceiling.** USB Power Delivery's long-standing fixed voltages are 5 V, 9 V, 15 V and 20 V, and the USB Promoter Group notes that reaching 100 W needed 20 V over a cable rated at 5 A.
- **Etiquette is a real skill.** Buy something, ask, feed three devices from one socket, and never walk away from charging gear.
- **A town day is a charge day.** Mark likely sockets on the route the way you mark water.

</Highlight>

<SectionDivider variant="trail" />

## Charging on Route: Where the Sockets Actually Are

Sockets follow seated customers. Anywhere a business expects you to stay half an hour has power near the chairs; anywhere it expects you to keep moving does not. That one rule predicts most of the map.

| Place | Why it works | How reliable |
|---|---|---|
| Cafe or small-town diner | Seated customers, long dwell time, staff used to laptops | Good, if you buy something |
| Public library | Free, sheltered, staffed, usually quiet | Good, but policies vary and some limit charging time |
| Laundromat | You are there for an hour anyway, and sockets are plentiful | Good, though many are unattended |
| Campground shower or laundry block | Shaver and cleaner sockets near the sinks | A coin flip. Some are shaver-only or switched off |
| Grocery store with seating | Deli counters and in-store cafes often have outlets | Variable. Plenty have seating and no power |
| Visitor centre, park or trailhead building | Built for people waiting around | Good when open, which off-season may be rarely |
| Transit station | Waiting rooms and platforms increasingly have USB points | Variable, and USB-A points are often slow |
| Hotel, hostel or host | Every socket you want, overnight | The best charge of the trip. Plan around it |
| Bike shop | Sympathetic staff, and you may be buying a tyre | Ask. Never assume |

One honest warning about the outdoor ones. Exterior sockets on pavilions, restrooms and picnic shelters are often switched off at a panel inside the building, or removed entirely, and nothing about the faceplate tells you which. Treat any socket outside as a bonus, not a plan.

Libraries deserve their reputation, but they are not a free-for-all. One US public library's Electrical Devices and Outlet Usage Policy, approved by its board of trustees in January 2025, states that "Library outlets are primarily intended for library use" with "some limited use by the public" allowed, that charging time may be limited to ensure fair access, and that unattended items may be unplugged by staff and held at the nearest service desk for seven days. It also requires chargers to carry certification from a recognised testing laboratory such as UL, ETL or CSA, and prohibits charging transportation devices including e-bikes.

<SectionDivider variant="rule" />

## The Etiquette, Which Almost Nobody Writes Down

This is our judgment rather than published rule, but it decides whether the next bikepacker through town gets a socket at all.

**Buy something.** A coffee and a pastry is the rent on a 40-minute charge, and it is cheap rent. **Ask first**, even where the socket is obviously public. A staff member who said yes will defend you later; one who found out when they tripped over your cable will not.

**Do not monopolise the one outlet by the door.** Most cafes have one socket that everybody wants. Taking it for an hour with a single phone is worse behaviour than taking it for an hour with a four-port charger that a stranger can share.

**Do not leave gear unattended.** Beyond theft, policies anticipate it: the library policy above lets staff unplug anything left alone, and the University of Central Florida Libraries' outlets policy states that patrons "may not unplug any library equipment" and that cords "may not be draped across aisles, exit pathways."

<Tip title="Carry a stubby extension and a short multi-port charger">

A short extension lead turns a socket behind a table leg into a usable one and lets the charger sit on the table. Paired with a multi-port charger, it converts a single outlet from something you claim into something you lend. The tradeoff: it is cable and plastic you carry every day for a convenience you use at town stops. We would take it on a route with regular services and leave it at home on a remote one.

</Tip>

## Arriving Ready: the Top-Up Rhythm

The rhythm that works is simple and almost nobody does it by default. **The wall charges the power bank. The power bank charges everything else, later, while you ride.**

The bank is the only item in your kit with the patience for a long, slow charge and the capacity to hold a whole day's budget. Your phone can be topped up in a tailwind. Your bank cannot be topped up from anything but a socket.

Arriving ready means the cables live in one pouch you can find without unpacking, the bank sits at the top of the bag rather than the bottom of a dry sack, and you know before you sit down which devices are low. Ninety seconds of digging is ninety seconds of charge.

When time is short, charge in the order that matters: the safety device first, then navigation, then the phone, then the luxuries. A [satellite messenger](/posts/best-satellite-messengers-bikepacking) is the one item where a flat battery changes the character of the trip rather than the comfort of it, so it gets the port before the headphones do.

<PullQuote>The wall charges the bank. The bank charges everything else, later, from a jersey pocket.</PullQuote>

<Warning title="Do not assume your bank will pass power through">

Using a power bank as a mid-point, charging it from the wall while something else draws from it, only works on banks designed for it. Anker's guidance is to look for "pass-through" or "power path" in the spec sheet, and warns that without that design the cell is charging and discharging at once, which stresses internal components, adds heat and slows both ends. The cost of getting this wrong is a stop where you thought you were charging two things and charged neither.

</Warning>

<SectionDivider variant="ornamental" />

## Speed Is the Real Constraint

A cafe stop is 40 minutes, not four hours, and that changes which hardware matters. Work the arithmetic with the inputs visible.

A 10,000 mAh bank holds roughly 37 Wh at a nominal 3.7 V. At 20 W input, 40 minutes delivers 20 multiplied by two-thirds of an hour, so about 13 Wh before any conversion loss, or around a third of that bank. The same 40 minutes from a 5 W brick is about 3 Wh, which is under a tenth. **The charger, not the stop, is what you are short of.**

Published charge times line up with that. Anker's guide to charging a 10,000 mAh bank gives 6 to 10 hours from a 5 V 1 A (5 W) charger, 4 to 6 hours at 5 V 2 A, and 2.5 to 3.5 hours from an 18 W or faster USB-C PD or Quick Charge source. Note that the same page elsewhere says "around 3 to 4 hours" for an 18 W or 20 W charger, so treat these as ranges rather than specifications. Our arithmetic agrees with the shape of them: 37 Wh at 18 W is a touch over two hours in theory, and real-world losses push it towards three.

Three hours is more than you get. So the useful question is not "how long to full" but "how many watt-hours can I recover in the stop I was making anyway", which is the same currency we use in [how much battery you actually need](/posts/bikepacking-power-budget-watt-hours). If your budget runs near 18 Wh a day, two 40-minute stops at 20 W roughly cover it. The same two stops at 5 W come to under 7 Wh, about a third of it.

## The Charger and the Cable

This is where a modest purchase buys real time. USB Power Delivery negotiates fixed voltages of 5 V, 9 V, 15 V and 20 V, and the USB Promoter Group's own announcement of PD revision 3.1 in May 2021 notes that before that update PD "was limited to 100W via a solution based on 20V using USB Type-C cables rated at 5A." Revision 3.1 added 28 V, 36 V and 48 V to reach 240 W, which is a laptop story. For us the whole game lives between 20 W and 65 W.

A gallium nitride multi-port charger in that band is small enough to forget about and lets one socket serve a bank, a phone and a head unit at once. The tradeoff is that **total output is shared, not multiplied.** j5create publishes a combination table for its 65 W three-port GaN charger showing that with all three ports occupied, the first USB-C port provides up to 45 W while the second USB-C port and the USB-A port share 5 V at 3.6 A. Retailer listings for other 65 W models show similar two-port splits, often 45 W plus 18 W or 45 W plus 20 W. Buy on the combination table, not the headline number.

The cable can undo all of it. The USB-IF's 5 A requirement for 100 W is the formal end of the scale, and explainers from cable vendors put the practical line lower: a 3 A cable at 20 V tops out around 60 W, and cables rated above that are supposed to carry an e-marker chip declaring it. The chain runs at the speed of its slowest declared link, so a 65 W charger, a thin unmarked cable from a petrol station and a fast bank will charge at the cable's pace. We would carry one known-good short cable per device plus one long one for awkward sockets, and treat the cheap replacement bought mid-trip as a temporary fix.

<SectionDivider variant="trail" />

## When There Is Genuinely Nothing

Some stretches have no answer. Four days between services, a shoulder-season route where the visitor centre and the campground laundry are both shut, a region where the grid itself browns out at night. There, no charging habit saves you and the fix is rationing, not hardware.

Rationing means doing less with the devices you have. Downloaded maps instead of live navigation is the biggest single lever, which is why [offline maps when you have no signal](/posts/bikepacking-offline-maps-no-signal) is a power article as much as a navigation one. Longer tracking intervals on the messenger, the head unit's backlight off, aeroplane mode between checks. We have a separate piece on device power management on tour coming in this series; the short version is that behaviour beats capacity on almost every trip.

Crossing borders changes the plug and sometimes the voltage. Reolink's plug-type reference lists most of Europe at about 230 V on Type C, E and F plugs, the UK at 230 V on Type G, Japan at 100 V, and North America at 120 V on the Type A and B plugs Japan shares. Most USB chargers are rated for 100 to 240 V, so a plug adapter is normally enough, but that rating is printed on the charger and is worth reading rather than assuming. Cold shortens everything too, so a winter route needs a bigger margin than the same distance in June.

If you find yourself planning three trips in a row around socket scarcity, the honest conclusion is that you have outgrown the stop-based system. That is the moment for [choosing between a dynamo hub and a power bank](/posts/dynamo-hub-vs-power-bank-bikepacking) rather than buying a fourth cable.

## Planning Charge Points Before You Go

Mark power the way you mark water. The resupply stops are already pinned when you build the route; add a note to each saying what socket you expect and how long you can sit there. Our [resupply guide](/posts/bikepacking-resupply-guide) covers the town-stop planning this attaches to, and the two jobs overlap almost perfectly. **A town day is a charge day.**

Check opening hours against the shoulder season, not the summer listing. Note a second option in each town, because the one cafe with sockets is shut on Mondays somewhere. And give yourself one deliberate long charge every few days, usually a hostel or motel night, where the bank goes to full rather than to adequate.

Then write the charging kit into your [packing list](/posts/bikepacking-packing-list-checklist) as one pouch with a known weight: charger, adapters, one cable per device, one spare. Treating it as a single item is what stops it quietly growing into four chargers and a tangle.

<SectionDivider variant="rule" />

## What We Would Do

On a route through populated country we would carry a mid-size bank, a 30 W to 65 W GaN multi-port charger, a short extension and good cables, then stop thinking about power. The system is a rhythm, not a trick: the bank drinks from the wall while you eat, the devices drink from the bank while you ride, and the next town is a day or two away.

The failure mode is not running out of sockets. It is arriving at a good one with a 5 W brick, a tangled bag and 25 minutes, and leaving with nothing meaningful gained. Fix the charger, fix the pouch, and the sockets take care of themselves.

For how this fits with power budgeting, dynamo systems and the rest of the kit, start from [our bikepacking power and charging guide](/posts/bikepacking-power-charging-guide).


Charging Without a Dynamo: Finding Power on Route


## Dynamo Hub vs Power Bank for Bikepacking: The Short Answer

Ride long days, for many days, away from sockets, and the dynamo hub wins. Ride short days or short trips, and the power bank wins. The crossover sits at roughly **six to seven hours of riding a day** and **about a week between mains outlets**. Below those numbers a dynamo cannot earn back its weight, cost or drag.

That is the whole decision, and it is not about money. It is about how many hours a day you actually turn the cranks. A dynamo is a generator with a fixed cost per hour of riding and effectively infinite range. A power bank is a fuel tank with zero drag and a hard bottom. Everything else in your [bikepacking power and charging setup](/posts/bikepacking-power-charging-guide) follows from which of those two things your route needs.

The uncomfortable version: a dynamo bought for a weekend trip is almost always the wrong purchase, and a dynamo bought for a month-long remote route is almost always the right one. Riders arrive asking which is better. Below a certain daily mileage the honest answer is that a dynamo cannot cover its own charging overhead, and above a certain trip length a power bank big enough to do the job weighs more than the hub.

<Highlight label="The short version">

- A dynamo is regulated to about **3 W at 6 V** on most modern hubs, and Schmidt quotes **65 percent efficiency, but only at 15 km/h**, according to Wikipedia's hub dynamo entry.
- CyclingAbout's lab rig measured a Shimano UR700 producing **4.2 W at 15 km/h** at its maximum power point, but only **2.8 W at the same speed** through a real Forumslader V6 charger.
- The same test found a phone's **2.5 W charging threshold** needs about **13 km/h** with the best hub and charger pairing, and up to **18 km/h** with a worse one.
- Busch+Müller's own USB-Werk documentation says a dynamo supplies about **3 W at 15 km/h** while some phones draw **up to 5 W**, which is why a cache battery is not optional.
- Anker's own arithmetic turns a **10,000 mAh** bank into **37 Wh** and then into about **6,068 mAh at 5 V** once conversion losses are counted. Call it **30 Wh usable**, not 37.
- At a modest **20 Wh a day**, one month off-grid needs roughly **3.8 kg** of power banks. That is the point where the hub stops being a luxury.

</Highlight>

<SectionDivider variant="rule" />

## What Each System Actually Is, and What Each One Costs

A hub dynamo is a small alternator built into your front hub. Most modern hubs are regulated to about 3 W at 6 V, with some reaching 6 W at 12 V, according to [Wikipedia's hub dynamo entry](https://en.wikipedia.org/wiki/Hub_dynamo). On its own it produces wild AC, so a dynamo-to-USB regulator converts and smooths it into something a device will accept.

Its costs are three, and only one is obvious. First, capital: hub, regulator, and usually a cache battery. Second, a wheel rebuild or a new front wheel, because the hub is the wheel. Third, drag — a real, permanent tax on every hour you ride.

That drag has been measured. CyclingAbout's lab test, which spins a dynamo wheel against a motor on a steel plate and subtracts a non-dynamo baseline, found drag with lights and chargers off running from **1.4 W to 1.9 W for a SON 28** across 10 to 30 km/h, against 1.9 W to 5.2 W for an SP PD-8 and 1.4 W to 4.5 W for a Shimano UR700, with the figures accurate to within about 1 W ([CyclingAbout](https://www.cyclingabout.com/dynamo-hub-power-drag-testing-schmidt-son-shutter-precision-shimano/)). Switch a bright light on and the load climbs steeply — the same rig reported 14.5 W at 15 km/h for a UR700 driving a Busch+Müller IQ-X.

A power bank is a sealed lithium cell with a converter on the front. Its costs are simpler: carried weight, a hard capacity limit, and the logistics of finding a socket. Its great virtue is that it adds exactly zero drag. Nothing it does slows you down.

<PullQuote>A dynamo charges you by the hour. A power bank charges you once, in grams.</PullQuote>

<SectionDivider variant="trail" />

## The Dynamo Case: Output at Realistic Touring Speeds

Dynamo output is a function of wheel speed, and the numbers at touring speed are smaller than most riders expect. CyclingAbout's rig measured a Shimano UR700 at its maximum power point producing 1.5 W at 5 km/h, 2.6 W at 10 km/h, **4.2 W at 15 km/h**, 6.0 W at 20 km/h, 7.7 W at 25 km/h and 9.1 W at 30 km/h.

That is the theoretical ceiling. Through an actual charger you get less. The same test put a Forumslader V6 on that hub and measured 2.0 W at 10 km/h, **2.8 W at 15 km/h** and 4.7 W at 20 km/h. The honest planning figure for a loaded bike at a genuine 15 km/h is therefore under 3 W, nowhere near the 9 W you see on a fast descent.

Output also plateaus. Hubs are regulated, so once you are above their rated speed you are not harvesting proportionally more. Retailer listings for the SON 28 state it reaches rated output at about 16 km/h in a 700c wheel, against about 19 km/h for the lighter SONdelux ([SJS Cycles](https://www.sjscycles.co.uk/hubs-front/son-28-centre-lock-disc-dynamo-front-hub-polished-36-hole)). The practical consequence is that a dynamo rewards *duration*, not speed. Eight slow hours beats two fast ones.

<Tip title="Without a cache battery, riders conclude the dynamo does not work">

A dynamo does not charge a phone well directly, and this is the single most common disappointment. Busch+Müller's documentation for the USB-Werk explains the mechanism plainly: the dynamo supplies only about 3 W at around 15 km/h while some phones draw up to 5 W, so a buffer battery charges first and the USB output stays off until it reaches a set level. When the phone pulls the buffer down to its minimum, the output switches off again and the buffer refills, which "leads to interruptions, which some USB devices indicate with the charge start sound" ([bike-components product documentation](https://www.bike-components.de/en/busch-mueller/USB-Werk-Mobile-Charging-Device-p35972/)). The same source notes the buffer needs roughly 20 minutes above 17 km/h with nothing plugged in and the lights off to fill completely. Buy the hub and the regulator and skip the cache battery, and every stop sign undoes your charging.

</Tip>

What the dynamo genuinely buys you is range that does not run out and lights that never die. On a route where resupply is food and water only, that is worth real weight. We will cover the hub choice itself in the best dynamo hubs for bikepacking, and the regulator choice in the best dynamo USB chargers, because the charger matters at least as much as the hub — the measured gap between pairings is the difference between charging a phone at 13 km/h and needing 18 km/h.

<SectionDivider variant="ornamental" />

## The Power Bank Case: Usable Capacity Is Not Rated Capacity

For most trips, the power bank is the correct answer, and it is not close. The tradeoff is that you are carrying every watt-hour you will use, and when it is gone it is gone.

Start by distrusting the number on the case. Anker's own support page works it through: a 10 Ah cell at 3.7 V is 37 Wh, which at 5 V is 7.4 Ah, and after conversion losses at "typically around 82 percent efficiency" the effective capacity a device can use is about 6,068 mAh ([Anker](https://service.anker.com/article-description/Why-Is-the-Rated-Capacity-Marked-on-a-Power-Bank-Lower-Than-Expected)). Converting that back to energy with `Wh = mAh / 1000 x V` gives 6.068 Ah at 5 V, or **about 30 Wh of usable energy from a 10,000 mAh bank** — roughly 60 percent of the headline 10,000 mAh.

Now weigh it. Retailer listings put Anker's PowerCore II 10000, a 37 Wh bank, at **195 g** ([Galaxus](https://galaxus.be/en/s1/product/anker-powercore-10000-mah-18-w-37-wh-powerbanks-10285520)). Against 30 Wh usable, that is about **6.4 g per usable watt-hour**. That single number is the one to carry around in your head, because it converts any power budget directly into grams.

The power bank also wins on every failure mode that matters. It works at 0 km/h, while you sleep, in a tent, on a bus. It has no spokes to true and nothing to short out in the rain. If you are choosing the bank itself, we go through capacities and ports in our guide to [picking a portable charger for your phone and GPS](/posts/navigating-with-power-the-best-portable-charger-for-your-phone-and-gps).

<SectionDivider variant="trail" />

## The Crossover: Show the Sums

Pick a daily draw. We will use **20 Wh a day** as a worked example — a phone topped up, a head unit kept alive, and a light or two. Your real figure may be half or double that, and getting it right is the whole exercise, so start with [how much battery you actually need](/posts/bikepacking-power-budget-watt-hours) and substitute your own number into the sums below. Head units vary enormously in appetite; our round-up of [cycling computers for bikepacking](/posts/best-cycling-computers-bikepacking) is a reasonable place to see the spread.

**Break-even in riding hours.** At the measured 2.8 W a Forumslader V6 delivered from a UR700 at 15 km/h, covering 20 Wh takes `20 / 2.8`, about **7.1 hours of riding a day**. Push to 20 km/h and the measured 4.7 W cuts that to about **4.3 hours**. Drop to 10 km/h and the measured 2.0 W pushes it out to **10 hours**. A three-hour evening ride at 15 km/h yields about 8.4 Wh — under half a day's budget. This is why a dynamo on a weekend trip is a net loss.

**Break-even in grams.** At 6.4 g per usable watt-hour, 20 Wh a day costs you about **128 g of power bank per day**. Schmidt lists the SON 28 hub itself at about 440 g, so on hub mass against bank mass the batteries overtake the hub at roughly `440 / 128`, about **3.4 days**. Be honest about that figure, though: the dynamo system also needs a regulator and a cache battery, and you only pay the *difference* between the dynamo hub and the plain front hub it replaces. Add those back and the real mass crossover lands closer to **a week of genuine off-grid riding**.

| Trip | Energy needed at 20 Wh/day | Power banks, approx. | Our call |
|---|---|---|---|
| Weekend, 2 days | 40 Wh | ~260 g | Power bank, no argument |
| One week, a socket mid-trip | ~60-80 Wh carried | ~400-500 g | Power bank |
| One week, no sockets at all | 140 Wh | ~900 g | Dynamo if you ride 6+ hours daily |
| One month off-grid | 600 Wh | ~3.8 kg | Dynamo |
| Remote and open-ended | unbounded | impossible | Dynamo, only answer |

The bottom row is the real case for a dynamo. It is not that the hub is lighter on a given trip — it is that a dynamo's capacity does not have a bottom, so a route with no known end does not have a battery calculation at all.

<SectionDivider variant="rule" />

## When the Answer Flips Regardless of the Maths

**Cold.** Battery capacity falls in the cold while a generator does not care.

<Warning title="Expect to lose roughly half your capacity in deep cold">

Battery University states that a battery delivering 100 percent capacity at 27 °C typically delivers about 50 percent at -18 °C, and that most batteries sit near 50 percent performance at -20 °C, though the shortfall is temporary and recovers at room temperature ([Battery University](https://batteryuniversity.com/article/bu-502-discharging-at-high-and-low-temperatures)). Plan a winter power budget on your bank's rated capacity and you can be short by a wide margin on the coldest morning of the trip. Sleeping the bank inside your quilt is the standard mitigation, and we go further into cold-weather behaviour in our [winter bikepacking guide](/posts/winter-bikepacking-cold-weather-guide).

</Warning>

**Very slow or technical riding.** Dynamo output tracks wheel speed, and CyclingAbout's test found the 2.5 W smartphone charging threshold requires about 13 km/h with a UR700 and an Igaro D1, rising to about 17 to 18 km/h with other hub and charger pairings. A route averaging 9 km/h on chunky doubletrack may spend most of the day below the threshold entirely.

**Hike-a-bike.** Pushing generates nothing. A route with hours of carrying per day is a power bank route no matter how many days it lasts.

**Electrically hungry setups.** If you are running a bright dynamo light *and* charging, you are splitting a very small budget. For most riders, a rechargeable light plus a bank is simpler than a dynamo trying to do both, and our [overnight bike light round-up](/posts/best-bike-lights-overnight-bikepacking) treats that choice directly.

**The device that must not go flat.** If a [satellite messenger](/posts/best-satellite-messengers-bikepacking) is your emergency plan, it gets its own reserve. Neither system changes that.

**Not wanting to rebuild a wheel.** This is a legitimate reason, not a failure of nerve. A dynamo means a wheel build or a new front wheel, plus a connector that has to survive weather and vibration. Some riders simply do not want another system to maintain, and that preference is worth more than a few grams.

<SectionDivider variant="ornamental" />

## What We Would Do

**Weekends and sub-week trips with any socket access.** A power bank, every time. At about 6.4 g per usable watt-hour, two or three days of autonomy costs a few hundred grams. The tradeoff is that you are rationing from day one, and on a long cold weekend you may ration harder than you expected.

**One to two weeks, mostly rural, occasional cafes.** Still a power bank — one larger bank, charged at every opportunity. The tradeoff is route dependence: your charging plan is now a list of places that have to exist and be open.

**One month or longer off-grid, 6 or more riding hours a day.** The dynamo, decisively. At 20 Wh a day, a month of carried battery is roughly 3.8 kg, and no hub weighs that. The tradeoff is 1.4 W to 1.9 W of permanent drag on a good hub, plus the capital cost and a wheel build — and you still carry a cache battery.

**Open-ended or expedition routes.** The dynamo, and it is not really a comparison. The tradeoff is complexity in a place where a failed connector is genuinely inconvenient, so carry a small bank as backup regardless.

**Short, slow, technical riding or heavy hike-a-bike.** A power bank, even on long trips. The dynamo simply will not spin fast enough to pay.

The useful reframe is that these are not competitors. A dynamo is a slow trickle that never stops; a bank is a fast reserve that does. Most riders who end up with a hub still carry a bank, which tells you what each thing is actually for. For the full system — budgets, device draw, cables and chargers — see [our complete guide to bikepacking power and charging](/posts/bikepacking-power-charging-guide).


charging

How Much Battery Do You Actually Need? Bikepacking Power Budgeting

Bikepacking Power and Charging: The Complete Guide to Staying Charged Off-Grid

Charging Without a Dynamo: Finding Power on Route

Dynamo Hub vs Power Bank: Which Bikepacking Charging System Suits Your Trip