Low-voltage cutoff

Low-voltage cutoff is a protective setting, usually adjustable, that automatically shuts off a 12V fridge or other accessory once the connected battery's voltage drops to a chosen point, before it falls so low the engine cannot start. It exists specifically because compressor fridges and other always-on devices can otherwise run a car battery flat overnight.

Most 12V fridges offer at least a low, medium, and high cutoff setting, corresponding to roughly how much reserve capacity is preserved for starting the engine afterward. Running the fridge directly off the starting battery without a dual-battery setup or isolator makes this setting far more important than it would be when powering the fridge from a separate portable power station.

A common mistake is leaving the cutoff on its lowest, most permissive setting to keep the fridge running as long as possible, then finding the car will not start the next morning. If you regularly camp off the starting battery, set the cutoff conservatively and consider a jump starter as a backup rather than relying on the setting alone.