Backup Batteries and Main Battery Disconnect

Backup batteries sometimes referred to as auxiliary or supplemental batteries, serve an important role in maintaining power for certain vehicle systems even while the 12-volt battery power is cut. The backup batteries can aid in emergency situations by maintaining power for features like GM OnStar, Toyota Safety Connect System, and FCA Assist to name a few.

These batteries are not to be confused with vehicles that have more than one battery, like many hybrids. These types of backup batteries are often part of another module or part. Typically, the backup battery cannot be recharged and must be replaced if depleted. Which is why it is important to know whether the vehicle being repaired has a backup battery for a certain system and how to properly disconnect the main 12 V batteries prior to repairs. Battery disconnect procedures can be found within the vehicle specific service manual.

For example, per the 2019 Chevrolet Equinox service manual:

“For Vehicles equipped with OnStar® (UE1) with Back Up Battery: The Back Up Battery is a redundant power supply to allow limited OnStar® functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar®module). Do not disconnect the main vehicle battery or remove the OnStar® fuse with the ignition key in any position other than OFF. Retained accessory power should be allowed to time out or be disabled (simply opening the driver door should disable retained accessory power) before disconnecting power. Disconnecting power to the OnStar® module in any way while the ignition is On or with retained accessory power activated may cause activation of the OnStar® Back-Up Battery system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The back-up battery is not rechargeable and once activated the back-up battery must be replaced.”

This is just one example, the proper procedures to disconnect a battery can vary for each vehicle. Always follow OEM procedures and warnings to ensure a complete, safe, and quality repair.

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