Auxiliary batteries vary in size and specification dependent on the demands placed on it by the vehicle electrical system and can be used as a safety back-up to support the main battery when required or to provide voltage for specific vehicle systems all of the time.
Instead of using an alternator to charge the auxiliary battery like gas-powered vehicles do, auxiliary batteries in HEVs and EVs are recharged by the HV battery using an inverter/converter. Batteries in gas-powered vehicles are charged via the engine and alternator.
The auxiliary battery supports all 12v electrical systems: The exceptions are the air conditioning and heating systems. An auxiliary battery can also be used as a safety backup to support the main battery when required or to provide constant voltage for specific vehicle systems.
Modern vehicles with CO2 reduction technologies, high levels of specification, and new electronic driver aids may feature an auxiliary battery alongside the main vehicle starter battery or high voltage system battery on Hybrid and electric vehicles.
By fulfilling a dedicated role in powering accessories and devices, the auxiliary battery enhances the overall functionality, convenience, and resilience of vehicles, boats, and off-grid setups, making it an indispensable component in diverse energy systems.
Auxiliary batteries, like your main battery, need to be checked regularly for corrosion, damage and leakage. Depending on the location of the battery, this could be difficult for you to do yourself and you may require the assistance of a mechanic. What Are the Signs of a Bad or Failing Aux Battery?