RealTesla

Erm, that's not the issue. Gasoline cars have gasoline in the tank, meaning its very easy to estimate how much fuel you have left. In fact its not an estimate at all, its a direct measurement of gasoline in the tank.

The charged electrons inside a Li-ion battery? No good estimate methodology. I'm serious. You can't measure with a dipstick, there's no float-bob, you can't weigh, you can't do jack diddly shit with Li-ion batteries from any physical perspective.

What Li-ion estimations are is something called "coulomb counting". You count the electrons in, and count the electrons out. Guess what? It gets inaccurate when things like internal-leakage changes based off of the temperature changes over the past week and a half of charging. This is why phone Li-ion batteries can shutoff at "10%", because those electrons leaked out in a way that the colomb-counting sensor was unable to detect. (Many, many different sources of leakages).

Its like trying to measure the amount of gasoline in your tank by simply measuring the gasoline in and out of a gas-tank. But what about evaporation? What about a whole slew of other issues? You just can't plug all leaks in gasoline tanks or Li-ion. But you can just weigh the gas-tank to figure out how much gasoline is there, or you can have a float-bob that tells you how far the gasoline is from the bottom of the tank directly. But literally no such technology exists (or ever existed) for Li-ion.

Maybe in the future this could be invented. But this "last bit of charge phantomly disappeared" is almost innate to battery-tech, at least with today's level of technology.

In fact, measuring the "zero point" of any battery is famously one of the most difficult problems in battery tech. The only way that seems to reliably work is by discharging the battery all the way to 0% so you know for sure where it is. But otherwise? Good luck finding it (and you shouldn't discharge to 0% because it damages the battery anyway). So the columb-counting methodology gets less-and-less accurate over time as all of these leakages or other problems add up... and since the 0% point is rarely reached, there's almost no way to calibrate in practice.