The charge time of a power bank depends primarily on its battery capacity and the charger's output current.

Please remember the following estimation formula:

Charge time = (power bank battery capacity ÷ charger output current) x factor.

For batteries 10,000 mAh or less, use a factor of 1.2; for batteries 10,000 mAh or more, use a factor of 1.3. (Lithium batteries lose energy during charging, so the actual charge time is longer than the theoretical time. Therefore, we need to multiply the charge factor when calculating the charge time of a power bank.)

For a 10,000 mAh power bank using a 5V-2.4A charger, the charging time is 10 ah/2.4A x 1.2 = 5 hours.

If you're using a fast-charging charger or a power bank that supports fast charging, the estimation formula will be slightly different.

Charge time = (power bank rated energy ÷ charger wattage) x factor.

Power banks typically have their rated energy marked on them.

Charger wattage depends on the voltage and current.

For example:

How long does it take to fully charge a power bank with a 20,000 mAh battery using a fast-charging charger?

9V 1.5A charger ≈ 74Wh ÷ (9 x 1.5)W x 1.3 = 7.13h

12V 1.5A charger ≈ 74Wh ÷ (12 x 1.5)W x 1.3 = 5.34h

Have you figured it out?

This is just a rough estimate, suitable only for estimating the battery life of a power bank. Due to varying charging environments, actual charging times may vary.