What is an auxiliary battery?
An auxiliary battery is a secondary or backup power source that you can find in some vehicles. Luxury brands like Mercedes-Benz, Audi, and BMW usually have an aux battery.
Its purpose is to back up the primary battery. It sends power to parts of the car that operate while the engine is off, like the security system. Auxiliary batteries may also provide power to the engine start/stop system to ease the load on the main battery and alternator.
Auxiliary batteries are primarily found in cars with diesel engines, as diesel motors crank at a higher amp and require a high-resistance load to start. But you can also find auxiliary batteries in hybrids, electric vehicles
(EVs), and some luxury vehicles. How do I know if my auxiliary battery is faulty?
If your auxiliary battery is malfunctioning, you might notice some of these common symptoms:
You have trouble starting your car: The auxiliary battery acts as a backup power source for the car’s electrical system, and if your primary battery fails and can’t supply adequate power, and your auxiliary battery is faulty, the stop/start function in your car won’t work.
You notice leaks around the battery: The fluid in your battery is important to prevent battery cells from burning out. If you notice fluid leaking around your battery, you’ll need to get the battery replaced ASAP. Having this fluid leak into other parts of your engine can cause damage due to corrosion.
The battery light appears on your dash: A fully charged battery allows every component of a vehicle to function correctly. When the battery isn’t fully charged, these functions cannot work—or cannot work correctly. The battery light will usually illuminate when there’s an issue with the charging system.
The auxiliary battery lifespan for most cars is between five and eight years. If you have a vehicle between these ages that’s never had the auxiliary battery replaced, it may be time to have it inspected.
Remember: You can still operate your vehicle with a failing auxiliary battery, but it can put a strain on your primary battery, diminishing its life and necessitating premature replacement.
How often should an auxiliary battery be replaced?
Auxiliary batteries deteriorate over time, but the extent depends on your vehicle and how well you’ve followed a regular car maintenance schedule
. Most auxiliary batteries last between 5 to 8 years, though this can vary. Once your battery deteriorates, it will put a strain on other parts of the car and you may notice certain functions start to fail. If you think your auxiliary battery needs replacing, head to the mechanic immediately. Failing to replace a dead auxiliary battery can lead to serious vehicle damage.
Can I replace my auxiliary battery myself?
You might be able to DIY an auxiliary battery replacement if you’re confident in your auto repair skills. Not all vehicles have auxiliary batteries—but for those that do, the replacement process is similar to replacing an engine battery. If you’re not comfortable performing the process, leave the auxiliary battery replacement to a professional.