Battery Capacity Converter

def convert_battery_capacity(value: float, from_unit: str, to_unit: str,
                               voltage: float = 3.7) -> float:
    """
    Convert battery capacity between mAh, Ah, Wh, kWh.
    voltage is required for mAh/Ah <-> Wh/kWh conversions.
    """
    # Convert to milliwatt-hours as base
    if from_unit == "mAh":
        base_mwh = value * voltage
    elif from_unit == "Ah":
        base_mwh = value * 1000 * voltage
    elif from_unit == "Wh":
        base_mwh = value * 1000
    elif from_unit == "kWh":
        base_mwh = value * 1_000_000
    else:
        raise ValueError(f"Unknown unit: {from_unit}")

    if to_unit == "mAh":
        return base_mwh / voltage
    elif to_unit == "Ah":
        return base_mwh / (1000 * voltage)
    elif to_unit == "Wh":
        return base_mwh / 1000
    elif to_unit == "kWh":
        return base_mwh / 1_000_000
    else:
        raise ValueError(f"Unknown unit: {to_unit}")

# Examples
print(f"5000 mAh @ 3.7V = {convert_battery_capacity(5000, 'mAh', 'Wh'):.2f} Wh")
print(f"18.5 Wh = {convert_battery_capacity(18.5, 'Wh', 'mAh'):.0f} mAh @ 3.7V")
print(f"100 Wh = {convert_battery_capacity(100, 'Wh', 'kWh'):.4f} kWh")