mAh to Wh converter
The bank’s cells are 3.7 V and hold 37 Wh. The phone’s battery is also 3.7 V, but charging goes up to 5 V and back down, losing 10–20% as heat each way. So 37 Wh becomes about 31 Wh delivered, and a 5,000 mAh (18.5 Wh) phone gets roughly 1.7 charges, not 2.
Converts battery capacity in mAh to energy in watt-hours. The voltage is required because mAh is a charge and Wh is an energy — they are not comparable without it.
How to use the mah to wh converter
mAh measures charge and Wh measures energy, and energy is charge times voltage. That is why comparing two batteries by mAh alone is meaningless unless they share a voltage: a 5,000 mAh cell at 3.7 V holds 18.5 Wh, and a 5,000 mAh pack at 11.1 V holds 55.5 Wh — three times as much energy for the same headline number.
The conversion loss is the other half of the answer and it is why a power bank never delivers its rating. The cells sit at about 3.7 V, USB delivers 5 V, and the phone charges its own 3.7 V cell — so the energy is converted up and down again, losing ten to twenty per cent as heat each way. A 10,000 mAh bank marked 37 Wh realistically delivers around 31 Wh.
Watt-hours is the figure that matters for flying, which is the practical reason to convert. Airlines rate lithium batteries in Wh: under 100 Wh goes in cabin baggage freely, 100 to 160 Wh usually needs airline approval, and above 160 Wh is refused. A power bank labelled only in mAh has to be converted before you can tell, and manufacturers know this — which is why the Wh figure is often printed in very small type.
Questions
mAh is a charge and Wh is an energy. Energy is charge times voltage, so without the volts they are not comparable.