[samatman]

I'd argue that the undecomposed watt-hour is in fact the superior unit for batteries.

Because what I want to know about a battery is exactly how many hours I can use it at a given wattage. The voltage is determined by application, and the only amp-related stat I'm interested in is maximum current, which is more useful to me in watts anyway.

So a 50 Wh battery which I'm going to draw at 10 watts? five hours of use time. 20 watts? 2.5, and I can do this in my head all day. Joules are less convenient because going from seconds to hours is too annoying to do as mental maths.