Why mAh is a misleading number
A power bank advertised as "20,000mAh" will not deliver 20,000mAh to your phone. The mAh rating describes the internal battery cells at their nominal voltage (usually 3.7V) — but your phone charges at 5V or higher, and energy is lost stepping the voltage up. Real-world delivered capacity is typically 60–70% of the number on the box.
Worse, mAh alone doesn't tell you how much energy a power bank holds, because energy depends on voltage too. Two "10,000mAh" banks can hold meaningfully different amounts of energy. Comparing power banks by mAh is like comparing cars by the size of their fuel tank without knowing what fuel they use.
Watt-hours: the honest unit
Watt-hours (Wh) measure actual stored energy: Wh = (mAh × V) / 1000.
It's the unit airlines use for battery limits (100Wh carry-on cap), and it's
the only fair basis for comparing price across power banks. That's why the
default sort on this site is price per watt-hour ($/Wh) —
the lower the number, the more energy your dollar buys.
"Stated" vs. "estimated" Wh
Some manufacturers publish an exact Wh figure. When they do, we show it with a green stated badge — that number came from the manufacturer, not from us.
When a manufacturer publishes only mAh, we estimate:
Wh = (mAh × 3.7) / 1000, using 3.7V — the standard nominal
voltage of the lithium-ion and lithium-polymer cells used in nearly all
power banks. These rows carry a grey est. badge.
The 3.7V assumption has limits. A small number of power banks use LiFePO4 chemistry (~3.2V nominal), which would make our estimate slightly high for those products — LiFePO4 cells are heavier per Wh but more thermally stable and longer-lived. Where we know a product's actual cell voltage, we use it.
"Stated" vs. "estimated" output
Maximum output wattage works the same way. When a listing states an explicit wattage, it's shown with a green stated badge. When it isn't stated, we infer a conservative estimate from the charging standard mentioned (e.g. PD 3.0 → 20W, QC3.0 → 18W, nothing stated → 5W) and mark it with a grey estimate badge. Hover the badge to see the basis for the estimate.
Air travel and the ✈ carry-on safe filter
The ✈ Carry-on safe filter shows only power banks at or under 100 watt-hours. This is the threshold at which most national aviation authorities — including the FAA (USA), EASA (Europe), CAAC (China), and CASA (Australia) — permit lithium-ion batteries in carry-on baggage without prior airline approval.
Power banks above 100Wh are subject to varying rules: some authorities allow up to 160Wh with explicit airline approval and quantity limits; others are stricter. Batteries above 160Wh are generally prohibited in the cabin on commercial passenger flights.
The 100Wh filter is a starting point, not a guarantee. Individual airlines may impose lower limits or additional restrictions regardless of the general authority threshold. Always verify the rules with your specific airline and the aviation authority for every country you are departing from or transiting through before you travel.
Where the data comes from
Product data and prices are sourced from Amazon listings. Each row shows the date its price was last checked. Prices change frequently — always confirm before buying.
Listings are filtered automatically to remove accessories, cables, unrelated products, and items with implausible capacity claims. No filter is perfect — some good options may be missing due to listing errors, and some marginal listings may still get through. Established brands that trip a filter are held back for manual review rather than dropped outright, they may not appear in the table until reviewed. Solar chargers or power banks featuring solar cells are not listed because they require a far more complex evaluation, and it would interfere with the goal of a simple price-per-watthour comparison.
What we don't do
We don't test hardware, we don't accept payment for placement, and we don't rank by anything other than the numbers shown in the table. Every product link is an affiliate link (see About), but commission rates play no role in ordering — the table sorts purely on the data.