Why do some batteries use kWh to define the capacity and other batteries use mAh?

Question

Why do some batteries use kWh to define the capacity and other batteries use mAh?

In:

Answer 1

Well you can convert pretty easily between watts and amps if you know the voltage. It’s probably just tradition in how they rate themselves. For instance you wouldn’t expect car batteries and flashlight batteries to use the same scheme, would you?