By Larry Carley
Technical Editor

The condition of the battery as well as its state of charge are critical in late-model vehicles not only for reliable cranking and starting, but also for the onboard electronics. Low battery voltage can cause control modules to misbehave, or in some cases to go into a sleep mode and shut down. A dead battery is even worse because extremely low voltage or no voltage can cause some modules to forget learned data, adaptive adjustments or even programmed settings in their Keep Alive Memory chips. This, in turn, may require special relearn procedures to reset the forgetful modules after power has been restored, and/or reprogramming the module with a factory scan tool.

Disconnecting the battery in many late models to test, charge or replace a battery can be risky. So to save the memory settings, a battery backup should always be connected to the battery cables or a live power receptacle before disconn...