Current implementation of system.fill_battery_state only reads "charge_*" and "current_*" attributes. Some batteries expose different attributes, namely "power_*" and "energy_*". Added the required logic to support both types.
Further, when rewriting the function I also added support for systems with multiple batteries. Windows documentation was not clear but from what I gathered struct SYSTEM_BATTERY_STATE sets Charging and Discharging if ANY battery is charging/discharging. So, to check if the overall system is charging/discharging only Rate can be used.
Also cleaned the code related to "AC". There was a "fixme" there which I didn't fully undertand as SYSTEM_BATTERY_STATE.AcOnLine == True if any AC is present, so the proper logic was already implemented