Buying a Power Bank: How Many mAh Do You Actually Need?

Power banks are one of those products where a single big number on the box dominates the buying decision: the mAh rating. That’s only half the story.

Not all mAh are equal

The stated capacity of a power bank refers to the internal cells, not to what actually ends up reaching your phone. Voltage conversion typically loses 20–30% of the capacity. A 20,000 mAh power bank realistically charges a phone with a 4,500 mAh battery fully three to four times — not four and a half to five times, as a naive back-of-envelope calculation would suggest.

Watts determine charging speed

Capacity says nothing about how fast charging happens — that’s determined by the wattage. A phone with 20 W fast charging only benefits from that speed if both the power bank and the cable support that output. The weakest link in the chain sets the pace.

How much capacity do you actually need?

Usage profile	Recommended capacity
One phone, a day out	5,000–10,000 mAh
Phone + tablet, multi-day	15,000–20,000 mAh
Camping / travel without outlets	20,000 mAh or more

If you commute daily and just need an emergency backup for your phone, a big 20,000 mAh power bank usually means carrying more weight than you’ll actually use.

Our recommendations

For anyone who regularly charges multiple devices on the go, the VoltCore at 20,000 mAh has proven itself in our testing. For your desk or travel bag as a companion piece, we’d also recommend a compact GaN charger.