Buy a Power Bank: How Much mAh Do You Need?

Power banks are products where a single large number on the packaging often dominates the purchase decision: the mAh rating. That’s only half the story.

mAh Isn’t Always mAh

The stated capacity of a power bank refers to the internal cells, not what actually ends up charging your smartphone. When converting the voltage, 20–30% of the capacity is typically lost. A power bank with 20,000 mAh will therefore realistically charge a smartphone with a 4,500 mAh battery three to four times, not four and a half to five times, as a simple calculation would suggest.

Watts Determine Charging Speed

Capacity doesn’t tell you how fast it will charge – that’s determined by the Watt rating. A smartphone with 20W fast charging only benefits from that speed if both the power bank and the cable support that power. The weakest link in the chain determines the pace.

Charge Cycles: Why Your Power Bank Gets Weaker Over Time

Like any lithium-ion battery, a power bank also loses some capacity with each full charge cycle. After about 300–500 cycles, only 70–80% of the original capacity is often usable – with daily use, this is noticeable after about one to two years. If you don’t fully discharge the power bank and don’t leave it permanently at full charge, you can noticeably slow down this wear.

How Much Capacity Do You Really Need?

Usage Profile	Recommended Capacity
One smartphone, one day on the go	5,000–10,000 mAh
Smartphone + Tablet, multi-day	15,000–20,000 mAh
Camping / Travel without an outlet	20,000 mAh or more

If you commute daily and only need a backup for your smartphone, you often buy more weight with a large 20,000 mAh power bank than you actually use.

Our Recommendations

For anyone who regularly charges multiple devices on the go, we recommend the Anker Power Bank 20,000 mAh, 87 W. It offers a high capacity and can also charge laptops. The built-in cable is practical. However, note that a defective cable cannot be easily replaced. As a supplement for the desk or travel bag, we recommend the Anker 735 Charger (GaNPrime, 65 W). It charges multiple devices simultaneously and is compact thanks to GaN technology.