Estimates battery charge time given capacity in mAh, charge current in mA, charger efficiency, and initial state of charge. Accounts for real-world charging losses (typically 80-90% efficient) to produce time in hours and minutes, energy required in Wh (at an optional voltage, default 3.7V for Li-ion), and the C-rate of the charge. Useful for solar charge controller sizing, USB charging time estimation, lead-acid float charging, and EV battery planning. The C-rate output helps verify the charge current is within safe limits (typically 0.5C-1C for Li-ion). Chain from solar_sizing charge_controller_amps to size a solar charging system end-to-end.