Refactor: min/max voltage settings to guesstimate battery charge remaining runtime - promote runtimecal as one common solution/pattern #2420

Drivers like tripplite_usb have their own settings (e.g. 10% and 100% voltages) that would map well into runtimecal of other drivers.
Likewise, introduction of localcalculation with #1692 into riello drivers originally dealt with the idea that runtimecal should replace it.

Probably similar values appear in other drivers (these ones popped up during work on #2294).