How powerful of a power bank do you need to safely charge a laptop?

A power bank is more than its capacity. You also need to know how fast it can deliver power so your laptop doesn’t drain while it’s connected. How powerful of a power bank do you need to safely charge a laptop.

Two values explain the experience you’ll have: watt-hours (Wh) for capacity and watts for output. Power banks provide their capacities in milliamp-hours (mAh), but for a proper measure of capacity across devices (especially for a higher-drain device like a laptop), you need to multiply this value by the voltage to get the true amount of energy stored in watt-hours. Most power banks store energy in lithium-ion cells at about 3.7 volts (V).

Watts are equal to volts times amperes, and you must divide the mAh count by 1,000 since 1,000 mAh is one amp. So for example, a 10,000 mAh bank stores roughly 37Wh (3.7V x 10Ah) before conversion loss. Doubling the mAh doubles the Wh as long as voltage stays consistent, so a 20,000 mAh bank is about 74Wh.

Next, you need to know the Wh rating of your laptop’s battery, which you should be able to find on the manufacturer’s website.