A cell phone charger uses 4.83 joules per second. When plugged into an outlet but only 1.31 joules per second actually goes into the phone battery

Then there are another (4.83 - 1.31) = 3.52 joules per second (watts) that go

somewhere else. They become heat that makes the charger warm up while

it's working.

If these figures are accurate, then it's interesting to notice that the device

is almost 3 times as efficient when you call it a heater as it is when you

call it a battery charger.