Why Do Phones Heat Up When You Charge Them?

Phones get warm when you charge them because they're working hard. Like when you’re running and your body gets hot, the phone is doing a lot of work while it's charging, especially inside its battery. The parts that help move electricity around can feel like little engines turning on fire, which makes things warm. If you put your phone in a pocket while it’s charging, it might even feel like it’s cooking.