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.

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.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

how do you know if a car is vapor locked and how do you fix it?

It is very unlikely that a fuel injected engine is vapor locked (even at 108 degrees). From experience, an electrical component failed based upon heat and mileage of the vehicle. A code scanner will likely lead you to the issue....

Lights went out while driving

If fuses and relays are good, there are other possible causes. The ignition switch may have failed internally. If the circuitry inside the electrical portion of the ignition switch has a break or short, it can cut power to the...

We have a 2007 Honda CRV - new battery installed. While driving seeing sporadic light surge on Dash. Thoughts?

If you just had battery replaced due to it going dead then you may have a charging system problem if light is coming on. Have the charging system checked to see if you need an alternator or have another problem....

Related articles

How Do I Prepare My Car for Summer?
Summer's Summer's heat, dust, and stop-and-go traffic will take their tolls on your vehicle. Follow these tips to ensure optimum wellness of your car: Air Conditioning: Have your air conditioning inspected by a qualified technician. Newer models have...
The Best Used Cars to Buy If You're an Uber or Lyft Driver
Are Are you thinking of becoming a driver for Uber or Lyft? That could be an exciting career change – you’ll get to meet a lot of interesting people, and if you love to drive, what better way to spend...
How Long Do Wiring Harnesses Last?
Car wiring harnesses connect all the different electrical systems and components in a vehicle. Wiring harnesses can last the lifetime of the vehicle.