A charging system includes: an interface configured to removably and electrically couple to an external battery; a connector configured to removably and electrically couple to an on-board diagnostic (OBD) port of a vehicle; charge management circuitry electrically coupled to the interface and the connector; and a microcontroller unit (MCU) coupled to the charge management circuitry. The MCU is configured to execute computer readable program code for managing an output of current from the external battery to a vehicle battery of the vehicle through the electrical coupling of the connector and the OBD port. The charging system can be used to prevent a vehicle battery from becoming discharged during extended periods of storage.