Heh. It's called, "How much accuracy does one want out of electronics, anyway?"
Off the top of my head, temperature variations affect things like voltage references, components, and what-all. Further, working out Just How Many Electrons Are In Those Batteries is not, by any means, some kind of Solved Problem. It's not quite as bad as figuring out how much fuel is any kind of fuel tank, but it's not far off.
Just so we're clear on this: I've never had an ICE car that had an accurate fuel gauge. I mean.. stays at full for the first 50 or 100 miles, drops rapidly to 3/4 full, drifts downwards slowly, and still has two gallons left over when the needle's on "E". Turns out that a float, a resistance potentiometer attached to an arm, and some kind of reference isn't wildly accurate, to say the least.
Likewise, figuring out how many electrons have been dumped into a slew of individual cells, all with different levels of degradation, and varying voltages as a function of temperature Has Its Limits.