Power banks

Think in watt-hours, not milliamp-hours. The festivals do, and so do airlines. The conversion is simple: milliamp-hours times 3.7 volts, divided by 1,000. So 20,000 mAh becomes 74 Wh.

That is the number that counts at the gate. Defqon.1 allows at most 27,000 mAh — about 99.9 Wh — and additionally requires USB-only outputs: power stations with a 220-volt socket stay outside, and so do solar panels. Pick your festival above and we will flag every item that goes over.

And printed capacity is not delivered energy. In Stiftung Warentest's power bank test (issue 2/2026, 24 models) the differences in usable energy were wide enough to decide the ranking. Some charge is lost at every conversion — plan for the buffer instead of trusting the big number on the box.