Q: Can running the blowers for the AC with the engine off drain the battery?

asked by on September 09, 2016

I have gone out to my car on my 45-min lunch break several other times and used the radio and the AC blower fans to move the air in the car and have not had any issues with a dead/weak battery. Today I went out and used the blowers for about 45-min while I did some work on my laptop. It made the battery so weak that the starter motor would turn but not enough to crank the engine. I left the car sit for a few hours and when I left at the end of the day, it started fine. Will running the AC blowers really draw that much battery power to drain it that much? I've done it before with no issues until today. Any thoughts? Thanks!

My car has 11260 miles.
My car has an automatic transmission.

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The problem is although the current draw over 45 minutes might be "low", your battery might be weak, meaning it could have a bad cell and a low reserve capacity. It doesn’t take much to "drain" a weak battery. A confusing thing though is your car is only a year or two old thus making a weak (i.e., "old") battery hypothesis, well, weak. Nevertheless, the thing to do is have your battery load tested (any battery shop will do this for free) to determine its actual condition. If it passes the load test (ask for copy of results so you can see the margin by which it passed), it is possible you have excess current draw in your car’s electrical system. Also consider the possibility that during your most recent break, maybe you inadvertently turned the headlights on which would add to the discharge. Get your battery tested, and if it is OK but the starting difficulty returns, a certified technician from YourMechanic, can diagnose your electrical system.

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