Better battery level measurement for systems without fuel gauge
We have same rough idea since https://source.puri.sm/Librem5/linux-next/issues/65 where we guess the battery level (since there's no fuel gauge on the devkit) using a linear ocv (although we only have ccv).
We could improve this by something lie https://github.com/pavelmachek/libbattery/blob/master/libbattery.c which is better what we do in the kernel atm (we would have to guess/measure the discharge current though) since it doesn't seem to be available from the bq25890 either.