How prices per 100 Wh are computed
The mAh on the box says little about what a power bank costs. Labels print capacities at different voltages, some print two of them, and a two-pack is easy to count once. This site turns every Amazon power bank and power station listing into the price of the same thing — 100 watt-hours of battery energy — and ranks by that.
The price column
Every category is quoted per 100 Wh, about the energy of a 27,000 mAh power bank and the airline carry-on limit. Kinds of power bank are never ranked against each other: a magnetic bank, a laptop bank and a power station do different jobs.
| Kind | Categories | Energy priced | Output column | Example |
|---|---|---|---|---|
| Power banks | power banks, magnetic (MagSafe, Qi2), laptop, wireless, built-in cable, solar | mAh × 3.7 V, or the stated Wh where it agrees within 20 % | max. output, W | $25.99 for 20,000 mAh (74 Wh) = $35.12 per 100 Wh |
| Power stations | portable power stations | the stated Wh | AC output, W | $449 for 1,056 Wh = $42.52 per 100 Wh |
Why mAh × 3.7 V
A milliamp-hour counts charge, not energy. The headline mAh on a power bank is the charge of its lithium cells at their nominal voltage, 3.6 to 3.7 volts, so its energy is mAh × 3.7 ÷ 1,000 watt-hours: 20,000 mAh is 74 Wh, 10,000 mAh is 37 Wh. That is a convention, not an estimate — it is the voltage every headline figure is written at — so prices from it are not marked as estimates. It is also why a watt-hour is the honest unit: a phone charges at 5 V or more, and the same energy is fewer mAh there.
Rated capacity is never priced
Many labels print a second, smaller figure: “rated capacity 12,000mAh (5V/3A)” beside a 20,000 mAh headline. It is what reaches the USB port after the bank steps its cells up to 5 V and loses some energy as heat, usually about a third less. Sellers measure it differently or not at all, so it is shown in a row’s details but never priced: every bank is compared on its headline figure, measured the same way.
Stated watt-hours and the 20 % rule
Where a listing states watt-hours, they are used when they agree with mAh × 3.7 V within 20 %: cells rated at 3.6 V print a little less (Anker’s 24,000 mAh bank states 86.4 Wh). A figure further off is often the rated energy; it is set aside, mAh × 3.7 V is used, and the price is marked ~. A stated Wh less than half or more than double the mAh’s cannot describe the same battery, and the listing gets no price at all.
Power stations
A portable power station is priced on its stated watt-hours only. The mAh figures on station listings are marketing: some are counted at the 3.2 V of LiFePO4 cells, some at 3.7 V, some invented. Stations are grouped in three classes by energy — up to 400 Wh, 401–1,200 Wh and over 1,200 Wh — and their output column shows the rated AC output, never the surge or peak figure. A station sold with a solar panel is priced with the panel in the box.
Packs
“2 Pack” and “2 x 10000mAh” are two power banks in one offer: 2 × 37 = 74 Wh. A stated Wh that matches the pack’s total is read as the total. Ports, cables and colours are never a pack.
The output column and the highlights
Max output is the highest output the listing states, in watts: a laptop needs 65 W or more, a phone charges fast at 20–30 W. For a power station it is the rated AC output. Input ratings and surge, peak or boost figures are never shown there, and the column never changes the ranking. Best value marks the lowest price per 100 Wh among in-stock listings in the selected category that match your filters, across all result pages; Most powerful marks the highest output. Tied winners share the highlight, and a lone listing gets no badge.
What is estimated, and what never is
Two things make a price an estimate, marked ~ and removed by “Hide estimates”: a stated Wh that disagreed with the mAh and was set aside, and a title that names more than one capacity (the largest is used). A listing without a stated capacity is listed by package price, without a price per Wh.
Never estimated:
- a capacity from a model name — “PowerCore 10000” without “mAh” is a name, not a figure;
- a capacity from a power figure — “22.5W” and “PD 20W” are outputs, never capacity;
- a rated or usable capacity — it is never priced;
- a power station’s energy from its mAh — only its stated Wh counts.
Fake capacities
Listings claiming 50,000, 500,000 or 2,000,000 mAh for a few dollars are common. Three guards keep them out of the ranking: capacities outside 1,000–100,000 mAh are refused; a bank claiming more than 100 mAh per gram of its own weight claims more than any lithium cell holds; and a price per watt-hour far below the market (under 5 US cents per Wh for a power bank, 10 for a power station, converted from each storefront’s currency) is treated as a misread or a fake. Such listings stay visible, marked, without a price per Wh. That catches the obvious cases, not every one: buy from a maker or seller you trust.
Flying with a power bank
Under the IATA guidance most airlines follow, spare power banks travel in carry-on baggage only: up to 100 Wh without approval, 101–160 Wh with the airline’s approval (usually two at most), and none above 160 Wh. A 27,000 mAh bank is 99.9 Wh; power stations are far above the limit. This is information, not advice, and never checked against your flight: ask your airline. The mAh to Wh calculator converts any label.
What is not listed
Jump starters, phone battery cases, wireless chargers, pads and stands without a battery, cables, wall and car chargers, bare 18650 cells and AA batteries, UPS units, solar panels without a battery, expansion batteries for power stations, and cases and pouches are never listed, even when their titles name a capacity.
Where the numbers come from
Capacities, packs and outputs are read from the listing itself: the title (“Anker 737 Power Bank, 24,000mAh, 140W, 86.4Wh” → 24,000 mAh, 86.4 Wh stated, 140 W out) and, where the product page has been read, the description and product information. Every number read from a product page must come with the exact words it was read from, or it is dropped.
Data freshness & countries
Prices are refreshed weekly for each of ten Amazon storefronts, each a separate catalog in its own currency; the date above the table shows the last update. Prices and availability change at any time — what Amazon shows at checkout is what applies.
Affiliate disclosure
Product links carry an Amazon Associates tag. As an Amazon Associate, this site earns from qualifying purchases, at no extra cost to you. Rankings are computed from the numbers alone and are never sponsored.
Safety is your check
A cheap watt-hour is only a bargain from a battery you can trust. This site does not test or certify anything and never presents a listing as UL, CE, UKCA or PSE certified; check the marks with the seller. In Japan, mobile batteries must carry the PSE mark. Whether a bank charges your device at its full speed depends on the device’s charging standard (USB Power Delivery, Qi2, MagSafe).