what is power banks report capacity? mAh vs. rated capacity explained

Illustration for what is power banks report capacity

A 10,000mAh power bank has never charged a 5,000mAh phone twice, and the reason lives in the gap between two numbers: the capacity a power bank reports and the capacity it actually delivers through its USB port.

Direct answer: A power bank's report capacity — the big mAh figure printed on the box — is almost always the raw capacity of its internal lithium cells at their native 3.7 volts, not what comes out of the port. The figure that predicts real-world charging is the rated capacity (output at 5V), which typically lands at 60–70% of the reported number, or the watt-hour (Wh) rating that regulators now require on the label. In practice, expect roughly two-thirds of the printed mAh to reach your phone.

10,000mAh printed = 37Wh stored ≈ 6,000–6,600mAh actually delivered at the port
Buying rule: compare Wh or rated capacity, never the headline mAh
Flying rule (2026): under 100Wh — about 27,000mAh — is the carry-on ceiling

Chester Takau · AIGadgeTech
Chester Takau is an independent tech reviewer who synthesises professional testing data with real user experience to cut through marketing claims.

What "report capacity" actually means on a power bank

When a manufacturer reports a capacity, it is describing the battery cells inside the case. Lithium-ion cells have a nominal voltage of about 3.7V, so a "20,000mAh" bank is really a bundle of cells holding 20,000 milliamp-hours at 3.7V. Your phone, however, charges from a 5V (or 9V/12V/20V) USB output. Stepping 3.7V up to 5V costs energy, and that cost is exactly what the headline number hides.

Buyers actually meet three different capacity numbers, and no major brand reconciles them in one place:

The number you see	Where it appears	What it actually measures
Cell (battery) capacity — e.g. "20,000mAh"	Box headline, product title	Raw internal cells at 3.7V — the biggest, most marketable figure
Rated capacity — e.g. "12,500mAh (5V)"	Fine print, spec sheet	Real output available at the USB port — the honest number
Rated energy (Wh) — e.g. "74Wh"	Compliance label, airline rules	Total stored energy, independent of voltage — the only apples-to-apples figure

Part of the confusion is that labeling is voluntary in most markets: a box may quote the 3.7V cell figure or the 5V output figure with no hint of which one you are reading. Anker is the exception reviewers keep singling out, because it publishes rated capacity and efficiency figures alongside the headline mAh instead of hiding behind the cell number.

Why can't a 10,000mAh power bank charge my 5,000mAh phone twice?

Work through the energy, not the milliamp-hours:

Stored energy: 10,000mAh × 3.7V = 37 watt-hours.
Conversion loss: the boost converter steps 3.7V up to 5V at roughly 85–90% efficiency, leaving about 31–33Wh at the port — around 6,000–6,600mAh at 5V.
Second loss at the phone: the phone's own charging circuit, the cable, and heat shave off another slice before energy reaches the battery.

The net result is about one to one-and-a-half full charges of a 5,000mAh phone — not two. MakeUseOf's breakdown of power bank inefficiency walks the same chain of losses, and the short explainer below visualises why the printed numbers never survive contact with a real device:

Is mAh or Wh the number you should actually compare?

Watt-hours. Milliamp-hours are only comparable at the same voltage, and power banks quietly mix voltages — 3.7V on the box, 5V or higher at the port. Watt-hours remove the voltage from the equation entirely:

Wh = (mAh × volts) ÷ 1000 → a 20,000mAh bank at 3.7V stores 74Wh, full stop.

How-To Geek calls the headline-mAh habit a marketing "white lie" worth watching for when shopping for power banks, and frequent flyers increasingly agree that Wh is the more honest unit — the catch is that most boxes still headline mAh, so you end up doing the conversion yourself.

How much of the advertised capacity do you actually get?

The widely repeated rule of thumb is two-thirds, but buying guides put the real-world yield anywhere from 55% to 70% of the printed figure — the disagreement itself tells you how much depends on converter quality, cable, temperature, and cell age. Here is what the math looks like across the common size tiers, using 85–90% converter efficiency:

Printed cell capacity	Stored energy	Realistic output at 5V	Charges a 5,000mAh phone
4,500–5,000mAh	17–18.5Wh	~2,700–3,300mAh	roughly half a charge
10,000mAh	37Wh	~6,000–6,600mAh	about 1–1.5
20,000mAh	74Wh	~12,000–13,200mAh	about 2–3
25,000–27,000mAh	92.5–99.9Wh	~15,000–17,800mAh	about 3–4

Real results vary with cable quality, ambient temperature, and how many charge cycles the bank has aged through. The tiers line up with current picks in GearJunkie's best power banks guide, which added the 25,000mAh Anker Laptop Power Bank and the pocketable 4,500mAh iWALK in its May 2026 update — 27,000mAh sits deliberately just under the 100Wh airline ceiling (99.9Wh).

How do you check if a cheap power bank's advertised capacity is fake?

Physics is the fastest filter. Lithium cells are energy-dense but not magic: a genuine 10,000mAh bank weighs roughly 180–250g, a real 20,000mAh unit around 350–450g, and a legitimate 50,000mAh pack (185Wh) needs the better part of a kilogram of cells. A slim 250g listing on a marketplace claiming 50,000–100,000mAh is not optimistic — it is impossible, and buyers on forums flag these listings constantly.

Other tells: no rated capacity or Wh anywhere in the fine print, a price far below name brands of the same claimed size, and no recognizable certification mark. The same value-per-dollar scepticism drives our budget tech picks that are worth the price — cheap is fine, impossible is not.

For a bank you already own, the definitive check is a USB power meter: charge the bank fully, then discharge it through an inline meter into a device or load until cutoff. The meter logs exactly how many mAh and Wh left the port — the same quantity the rated capacity claims. A healthy unit lands within about 10% of its rated figure, i.e. roughly two-thirds of the printed cell mAh. This walkthrough on measuring real power bank capacity shows the full method.

What the 2026 rules force power banks to report

Regulators are quietly ending the mAh guessing game by standardising on watt-hours:

Air travel: ICAO approved an addendum to its 2025–2026 Technical Instructions in March 2026, and carriers including the Lufthansa Group's updated power bank rules now cap passengers at two banks, carry-on only, with no in-flight recharging. The threshold that matters is 100Wh — about 27,000mAh — which is exactly why reading the Wh line on your label matters more than the mAh headline.
Product labeling: China's CCC certification for power banks added a unique traceability QR code in March 2026, with full enforcement by March 2027, and certified labels must disclose rated energy in Wh — not just mAh — per Meenova's CCC certification guide. Whether mandatory labeling actually stops capacity fraud remains an open question, but traceable labels give regulators something to enforce against.

The safety stakes behind these rules are concrete. In April 2026, the CPSC re-announced the Casely wireless power bank recall after 28 more overheating and fire reports, including one fatality; roughly 32,400 XO "Poppy Power Trip" banks sold at TJ Maxx and Marshalls were recalled for fire and burn hazards; and about 7,400 Super Off-Road 12,000mAh solar banks were pulled over swelling and overheating risk. Honest capacity reporting and cell quality tend to come from the same manufacturers.

If you are assembling a carry-on kit around these limits, our travel tech packing list for 2026 shows where a compliant bank fits alongside chargers and adapters, and the broader travel tech guide pulls the connectivity and power pieces together.

Power bank capacity: frequently asked questions

Why does my power bank's mAh rating differ between the box, the label, and the display readout?

Because each number is measured at a different voltage. The box headlines cell capacity at 3.7V, the compliance label lists rated energy in Wh (and sometimes rated output at 5V), and a built-in display estimates remaining charge from the cells' voltage — still on the 3.7V basis. Same energy, three accounting systems.

Does a higher mAh rating always mean more usable charge?

Only at the same voltage. Two banks both claiming 10,000mAh can store different amounts of energy if their cells run at different nominal voltages. Wh removes the ambiguity — that is the number to compare.

How much of the advertised capacity do I actually get — is the "2/3 rule" true?

Roughly, yes. Guides put the real-world yield between 55% and 70% of the printed figure, and two-thirds is the most quoted middle. Expect about 6,000–6,600mAh at the port from a 10,000mAh bank, less as the cells age or in cold weather.

What size power bank is still allowed as carry-on under the 2026 airline rules?

Anything under 100Wh — about 27,000mAh — flies without airline approval. Banks between 100Wh and 160Wh usually need carrier sign-off, and larger ones stay home. The 2026 updates add a two-bank-per-passenger limit and ban recharging the bank itself in flight.

Why do only some brands disclose rated capacity?

Because disclosure is voluntary in most markets, and the cell figure is bigger and better for marketing. Anker is repeatedly cited as the exception that publishes rated capacity and efficiency figures. Regulation is catching up — China's CCC labels will require Wh disclosure and QR traceability with full enforcement by March 2027.

Sources

Updated September 2026.

Transparency note: This article was researched and written by Chester Takau with AI assistance for research gathering and drafting. All recommendations reflect the author's own editorial judgment.