An HVAC system to be installed in a vehicle comprises a battery management controller. The battery management controller comprises at least one connection for electrically coupling a first power source with a first voltage; at least one connection for electrically coupling a second power source with a second voltage; and a first memory storage device configured to record data collected by the battery management controller. The battery management controller is configured to run a temperature control system and to supply power to the temperature control system from a combination of the first and second power sources with a combined voltage, and wherein the second power source is disconnected when the combined voltage drops below a predetermined amount.