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

Single cell batteries are typically rated with mAh since their voltages are always the same. IE: Lithium batteries are almost always 3.7v. A, D and C batteries are always 1.5v (Or 1.2v for rechargeable ones). So watts don’t really matter as the voltage will stay the same.

Where as multi-cell batteries like those in hybrids and EV’s consist of several batteries wired together, which changes the voltage. These are usually rated with kWh since their voltages will often be different. Most EV’s use around 350VDC, and most non-plugin hybrids are around 250VDC.