In late-model vehicles, there may be an accessory battery separate from the starting or main battery. This accessory battery usually has the same maintenance interval as the vehicle’s main battery and is recharged from the alternator in the same way.
If your vehicle has an accessory battery, it’s likely not located in the engine bay. These are usually in the rear of the vehicle or underneath one of the passenger seats. Accessory batteries are usually 12 volts and resemble, though they may not be exactly like, a standard automotive battery. Because accessory batteries do not start the engine, they usually have a lower cranking amp rating and often have less material in the cathode and anode. Some may even use a chemistry other than the standard lead-acid used in most automotive batteries.
