Low battery bugfix: - when the battery is low, we have previously disabled the load, which caused the battery voltage to increase slightly, so we never switched the system off, and the load was switched on only for a brief periods of time. Now we have the following battery voltage levels: < 3.0 V: we do not enable the load, blink the status LED faster, and after 60 iterations, power the system off <3.0 V .. 3.15 V): we still enable the load, but switch the system off after 60 iterations of LED blink <3.15 V .. 3.45 V): battery is low <3.45 V .. 3.8 V): battery is OK >= 3.8 V: battery is fully charged