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Car Won't Start After Two Days of No Use

My girlfriend has a 2012 Jetta Sportswagen TDI that has a brand new battery in it. We put the new battery in this winter after her car was having a really hard time starting in the colder temps. It seemed to be fine for a few months, but has recently had a hard time turning over. If she doesn’t drive the car for 2-3 days (which is often during these days with the coronavirus and all) it will not start. The car sounds like it’s trying to turn over but it’s very, very slow. The lights on the dashboard are still coming on. Does this sound like it’s a battery issue again? Or could it be something else like the starter? I’m not super knowledgeable about cars (all my car knowledge comes from Car Talk) so any suggestions would be great.

Let me know if I can provide more info.

The battery is recharged by the alternator once it is started and driven. It needs to be driven a bit, maybe 20 miles to bring the battery up to full charge. Really short trips again and again means the battery gets discharged and never fully recharged.

Another point, turning the car OFF doesn’t mean it is completely OFF. A number of electronic devices consume a trickle of battery current when the car is off and sitting. If one of those devices gets a small short or doesn’t think is is time to “sleep” and draw very little current, it can run the battery down in 1,2 or 3 days. And it doesn’t take much! 0.5 amps is enough to prevent a start in 3 days.

All that said… Likely one or the other is the problem. If your girlfriend’s Jetta has an aftermarket stereo. subwoofer, remote start, alarm, nav system, I’d start there. A mechanic can run a parasitic draw test to find the culprit or you can start pulling fuses to the aftermarket stuff to find the bad part.

Excellent, I’ll see what I can figure out. This was great information thank you!

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A few days ago, somebody posted his battery-related woes in a different thread, and he couldn’t figure out why driving once around the block wasn’t keeping his battery charged.

My response in that thread was essentially the same as yours in this thread, and I told that person that he would be better-off not even starting the engine, rather than starting it and driving it once around the block, because that resulted in a net battery drain. He/she never reacted/responded to my post.

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I leave my battery disconnected.

Have you had the alternator tested? It may not be charging the battery.