Power bank capacity explained: mAh, watt-hours and real output

A power bank sold as "10,000 mAh" does not deliver 10,000 mAh to your phone. That headline describes the battery cells inside, at their own low voltage. What comes out of the USB port is noticeably less, because the voltage has to be raised to USB levels and some energy is lost as heat on the way. The fix is to compare banks by the energy they deliver at the output, in watt-hours (Wh), and to treat the "W" figure in the name as a measure of charging speed, not size.

Three numbers on the label#

Good specification sheets, such as Xiaomi's, carry three different capacity figures:

• Cell capacity, in mAh. The headline number, measured at the cells' own low voltage. For the Lite model below, 37 Wh over 10,000 mAh works out at 3.7 V.
• Rated energy, in Wh. The energy stored in the cells. This is the figure airlines care about.
• Rated capacity, in mAh at a stated output such as 5 V / 3 A. What the bank actually delivers at its USB port under that load.

Xiaomi explains the gap directly: rated energy is what the battery contains, rated capacity is what it can discharge, and the boost circuit that raises the voltage loses some energy in conversion (Xiaomi FAQ).

Two "10,000 mAh" banks compared#

Sources: P16ZM specifications and PB1067 specifications.

The output-energy row is a simple calculation: amp-hours times volts equals watt-hours. For the Lite, 5,500 mAh is 5.5 Ah, and 5.5 × 5 V = 27.5 Wh. For the 67W model, 6 Ah × 5 V = 30 Wh. Divide by the typical cell energy and you get the efficiency: 27.5 / 37 is about 74 percent, which is exactly the conversion rate Xiaomi publishes for the Lite.

Two lessons stand out. First, the 67W model stores only slightly more energy than the 22.5W one; the big number in its name is about how fast it can push power out, not how much it holds. Second, its cells are listed as 3,400 mAh because they run at 11.61 V. Comparing mAh across different voltages is meaningless; watt-hours put everything on the same scale.

How many phone charges?#

The rated output is energy leaving the bank, and your phone loses some more while charging. Xiaomi's own example: its 22.5W Power Bank 10000, with the same 5,500 mAh rated capacity as the Lite, charges a Mi 11 with a 4,600 mAh battery about 1.5 times (Xiaomi FAQ). That works out at roughly 18 Wh of bank output per full charge of a 4,600 mAh phone.

Use that as a calibration rather than a promise. Your phone, cable, screen use and temperature all change the result. The most reliable way to plan a trip is to measure:

1. Charge the phone to 100 percent and use it for a typical day of the trip, with navigation, photos and offline maps.
2. Note how much battery is left in the evening and how often you would have needed to top up.
3. Check how far a full power bank gets the phone back up.

Then size the bank to cover the days until your next reliable socket, with a margin.

Capacity or charging speed?#

They solve different problems. Capacity matters when you are away from mains power for days, on a long trek or a multi-night camp. Charging power matters when your chance to recharge is short: a 67 W bank can refill itself in about 1.3 hours from a suitable fast charger, against around 4.5 hours for the Lite, which is the difference between topping up over lunch in a mountain hut and not (P16ZM; PB1067). The 67W model's 20 V output also suits USB-C laptops. Fast charging only helps if your phone, cable and wall charger support the same fast-charging standards.

Flying with a power bank#

New international rules from the International Civil Aviation Organization took effect on 27 March 2026. Passengers may carry no more than two power banks, in cabin baggage only, individually protected. Power banks up to 100 Wh need no approval; those over 100 Wh and up to 160 Wh need the airline's approval. Power banks must not be recharged on board and should not be used to charge other devices during the flight (ICAO; UK CAA summary).

This is where the rated energy in Wh matters: both Xiaomi models, at under 40 Wh, sit comfortably below the 100 Wh limit. Airlines can apply stricter rules of their own, so check your carrier's page before you fly.

Cold nights and hot cars#

Both models specify an operating range of 5 to 35°C, and the rated figures assume you stay inside it. On cold nights keep the bank inside your jacket by day and in your sleeping bag at night. Do not leave it on a car dashboard in summer sun. Specifications and flight rules were checked on 8 October 2026.