Wh as the measure of energy and wh/mi or wh/km as a measure of efficiency are pretty much standard on all production EVs I've seen. Ah/mile makes no sense outside of a specific vehicle and should be outlawed (joking).
Now, estimating energy left (or, even better, range left) is not a trivial task. That is, there is more than one way how to skin this cat. Energy in vs. energy out (Coulomb counting) sounds like a good idea in theory but then there is a challenge of accounting for battery self-discharging affected by temperature, cell age, and tons of other factors that need to be accounted for.
Using voltage and chemistry discharge curves is a quick and dirty way to do it and it generally "works" well for what it is. Ultimately, all you need to know is if you can make it to the destination and you can tweak that riding more or less efficiently.
I am leaning towards the idea of continuous learning and running some statistical analysis based on historic energy use and distance traveled.
Powervelocity.com wrote:Ahs as a metric make sense only within a specific vehicle within the battery pack that never changes.
Agreed. My goal is to have a reliable SOC indicator when riding. I always use the same pack.
An accurate Whr measurement would work equally as well for a SOC indication. Since both voltage and current data are available, I guess it's just a matter of doing the right math.