Drain on car battery may be from modules not going to 'sleep'

by Jim KerrAuto Tech . Apr 12 2019

Question: I have a 2013 Buick LaCrosse, and after I returned from holidays (I was away two weeks), I came home to find my car battery was dead. It started with a boost and, after charging the battery, I had it tested and it was fine. What would cause my battery to go dead so quickly?

Answer: There are many electronic modules on newer vehicles and each of them uses a small amount of battery power to keep memories powered up. Normally, these modules are commanded to go into a “sleep” mode by a master module so they use very little power, but something as simple as keeping the keys in the ignition can prevent the modules from going to sleep when they should. It is also possible for a module to malfunction and not go to sleep when commanded. These faults can drain the vehicle battery in less than a week.

First, make sure there were no lights left on. A glovebox, trunk or underhood light can drain the battery in about one day. Your LaCrosse should automatically turn off these lights after a few minutes, but check them first.

You can have a parasitic drain test done on the vehicle, where current is measured at the battery connection while all the modules are asleep. It should be less than 25 milliamps drain and will typically be in the seven to 10 milliamp range. It can take several minutes for the modules to go to sleep, so the drain will be higher when you first test it. If after around 10 minutes, the drain is still higher than 25 milliamps, then either a module isn’t asleep or there is something on. Note: aftermarket remote starters or audio systems are often one of the causes of battery drains.

The dealer can monitor modules with a scan tool and see which ones are not going to sleep, so this can help with detecting the problem. Also, your battery is now about six years old. Batteries will often last about seven years. Any more than that is a bonus. Your battery may be on its last legs and be part of the problem.