In a general aspect, a battery pack can include a battery configured to supply power to a connected device and to receive re-charge power from a charger circuit. The battery pack can further include a current modulating circuit configured to modulate current of the battery between first and second supply terminals of the battery pack. The battery pack can also include a controller configured to provide voltage protection of the battery pack and charge current control of the battery using the current modulating circuit. The controller can be configured, while the battery is being charged, to compare, at the battery pack, a charge voltage setpoint of the battery pack with a desired charging voltage; modify, at the battery pack, the charge voltage setpoint to achieve the desired charging voltage; and provide the modified charge voltage setpoint from the battery pack to a connected device.