* show battery voltage, current, and power in live view header (the "totals")
* show battery current and power in extra card
* use soc and current precision in live view
* BatteryStats: do not knowingly publish invalid data: not all battery
providers know all values the base class manages. make sure to
prevent publishing invalid values.
Co-authored-by: Bernhard Kirchen <schlimmchen@posteo.net>
