I'm sure this is a stupid question but I can't find the answer.
iPhones have roughly a 6-7 Watt Hour battery according to multiple sources online.
They can also use a 5W or 10W charger (1Amp x 5V - or 2A x 5V) for charging - which I have observed that they reliably draw for the first few hours of charging (then of course, slow down over about 80% charge).
Even a 10W charger takes 3 or 4 hours to get to 80% from no charge. Doesn't that mean it should have a 30 or 40Watt Hour battery? What am I missing?