When a dual battery system is added to a vehicle, it is usually because accessories have been added to the vehicle that are not factory-standard, and the primary battery in the vehicle does not deliver sufficient power to drive these new accessories effectively. Understand that we’re not saying you need an auxiliary battery to power, say, a phone charger or a stand-alone GPS. It’s more like if you’ve converted a cargo van into a camper, and you’ve added a fridge, microwave, entertainment system… you get the idea. In that case, it can be highly advantageous to have one battery to deal with starting your vehicle, and another to operate your accessories. That way, once you’ve reached your campsite, you don’t have to worry about drawing power from your primary battery.

So, how long will your auxiliary battery last? Properly cared for and maintained, you can expect anywhere from 18 months to 3 years of life from an auxiliary 12-volt battery. Much will depend on frequency of use, and how well the battery is protected. Rough roads can cause the cells to break down, reducing the lifespan. Allowing it to drain to less than half of its rated capacity will also reduce the life of the battery. And of course, if you are parking your vehicle for any length of time, you should use a battery maintainer.

Signs that your auxiliary battery needs to be replaced include:

  • Accessories not operating properly
  • Accessories not working at all

If you think your auxiliary battery could be failing, have it checked. A professional mechanic can test your auxiliary battery, and replace it if necessary.

This article originally appeared on YourMechanic.com as How Long Does an Auxiliary Battery Last? and was authored by Valerie Johnston.


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