Power Bank Usable Energy Calculator

ENERGY INPUTS

Translate the label into usable energy

Use the power bank's printed cell capacity and voltage. USB output wattage is a separate constraint.

Printed capacityUse the capacity printed on the power bank, not a seller's rounded headline.Nominal cell voltageMany lithium-ion labels use 3.6V or 3.7V; copy the exact printed value.Conversion efficiencyUse a conservative estimate when the manufacturer does not publish measured efficiency.Target device batteryUse the target device's battery energy in Wh, not its charging wattage.Desired recharge countDecimal values are useful for a top-up target, such as 1.5 charges.

Why usable Wh is the comparison unit

The printed capacity describes cells at their nominal voltage. Conversion to USB output loses energy, so a recharge estimate needs both voltage and efficiency. For travel, use the product's printed Wh label and current carrier rules, not this estimate alone.

FAA PackSafe guidance says spare lithium batteries and power banks belong in carry-on baggage, gives 100Wh as the normal lithium-ion size limit, and says 101-160Wh spare batteries usually require airline approval. Airlines may be stricter.

Read the flight-safe power bank guide Check the FAA lithium battery guidance