Power Banks Explained: What mAh Really Means for Your Phone

A 10,000 mAh label does not mean 10,000 mAh reaches your phone. Capacity is rated at the battery's internal 3.7 volts, while phones charge at 5 volts, and conversion losses of 20 to 30 percent are normal. In practice a 10,000 mAh power bank delivers roughly 6,500 to 7,500 mAh, which is about one and a half charges for a phone with a 4,500 mAh battery. Check the output rating as well: 18 watts or more is needed for fast charging, and 45 to 65 watts if you want to charge a tablet or laptop. A USB-C port that works for both input and output keeps your cables simple. If you fly, airlines generally limit power banks to 100 Wh, around 27,000 mAh, and require them in carry-on baggage. Weight also matters, because a 20,000 mAh unit is close to 400 grams. Always charge the bank with the cable and adapter it was designed for, and avoid leaving it in a hot car.