> Consumers use batteries that are a specific voltage. Watt hours obfuscates this fact. So when a user tries to plug a 1.2v 40w/h battery into a 12v device that

> Consumers use batteries that are a specific voltage. Watt hours obfuscates this fact. So when a user tries to plug a 1.2v 40w/h battery into a 12v device that takes a 40 w/h battery, they will not know why it does not work. This is kind of sort of true for gadgets that take AA or AAA or maybe small lead acid batteries. They need a battery at a specific voltage (except they don’t — NiMH, carbon-zinc, alkaline, and Li (metal) batteries all tend to be interchangeable despite rather different voltages), and they consume roughly constant current. But many modern devices use fancy power supplies that consume roughly constant power. And, more relevantly to newer devices, how many consumers say “hey, that cool USB charger operates at 16V internally, so I want X mAh?” (Also, batteries have discharge curves, not constant voltages. But in mAh’s slight defense, the charge delivered from a battery is less likely to vary widely with different rates of discharge than the energy delivered.)