Power Bank Capacity, Watt-Hours And What Airlines Allow

Milliamp-hours are measured at the cell voltage

A 10000mAh power bank holds 10000mAh at its internal cell voltage, typically 3.7V per cell. Your phone charges at 5V or higher. Converting between them loses energy, and the honest way to express what a pack holds is watt-hours: the 10000mAh packs in this range are published at 7.7V / 38.5Wh. That number does not change with the conversion, which is exactly why regulators use it.

Why the usable figure is lower than the label

Between the cell and the phone there is a boost converter, a charging circuit in the phone, and heat. A realistic planning figure is that a pack delivers meaningfully less to the phone than its label suggests, and that wireless charging costs more again than a cable does. None of this is a defect, and a supplier who claims otherwise is not describing physics.

What airlines actually limit

Airline rules are written in watt-hours, not milliamp-hours, and they generally require lithium packs in cabin baggage rather than in the hold. Packs under 100Wh are usually carried without approval; above that, approval is needed, and above a higher threshold they are refused. Every pack in this range is far below 100Wh, which is one of the reasons 10000mAh and 20000mAh are the capacities that sell.

Put the watt-hour figure on the packaging

Most airport confiscations of power banks happen because nobody can read a watt-hour rating off the product. Printing the Wh figure on the retail packaging and on the housing removes the ambiguity at a security desk, and it is the cheapest piece of customer support a brand can buy in this category.

What this means for freight

Lithium cells travel as dangerous goods under UN38.3 with packing and labelling requirements that depend on the watt-hour rating. This affects the shipment, not the shelf. Card readers, OTG adapters and wall chargers carry no cell and are not affected at all.