Battery keeps draining, any ideas?

[Nathans_Dad]

All,

I have not had any issues with starting my 911 until about two weeks ago. I noted when I went out to start it up to change out the tires the battery was completely dead. No crank at all, no lights, nothing. I pushed the car out of the garage and jumped it and it started right up. Ran fine. Drove it to the tire shop to get the new tires on and let it idle for about 20 minutes while there thinking that would charge the battery enough to get it started again. It would again not crank after the tires were put on. Jumped it at the tire shop and drove it home.

I took the battery in to NTB the next day and bought a new one, the one that was in it was from 2003 so I thought it was time for a fresh battery anyway. Installed the new battery and it cranked right up, no problems. I drove it that night and no issues then either. I parked it in the garage last Saturday and did not start it again until today when it again would not crank at all, completely dead NEW battery.

I was originally thinking alternator but it doesn't make sense that a completely fresh battery would drain over the course of a week just sitting there. I am wondering if there is a short somewhere or something that is running and draining the battery while it is sitting there.

Any ideas of where to start looking?

[kevin993]

I had that once and it turned about to be a climate control ECU unit that failed and kept drawing on the battery even when the car was not running. Mine is a 1997, so different model year but it took a long time to trouble shoot and figure out the issue. The car was fine after the unit was replaced.

[otto in norway]

Check your interior lights, including under the front lid.
You can measure the current drain with a simple multimeter. (If you know how to work it)
Then it's a simple elimitation process of removing fuses until you see the current drops. That will tell you where to look.

[jrbennett]

I've seen the power window relay kill a battery.
If you can open and close your windows with the key off (after openng a door) the relay is staying on.

[HarryD]

You will need to track down the draw.

Pull all of your fuses and put an ammeter on your battery lead.

You should see a Zero amp draw.

Reinstall each fuse and then check the draw again. If it increases, look for a short in that circuit. A few circuits will have a draw all the time like a clock.

Good luck, be patient.

[DRACO A5OG]

If I may suggest get a battery tender like the C-tek 3300, not only will it keep it charged it will also maintain it.

Driving her once a week may not be enough to keep the minimal charge required for our 3.2's.

Before you start her, get a reading and after a drive. Check the bentley manual to check the alternator and power to the starter

I found my positive terminal at the battery had a crack and was not properly re-charging my battery.

Jim

[porwolf]

Originally Posted by HarryD

You will need to track down the draw.

Pull all of your fuses and put an ammeter on your battery lead.

You should see a Zero amp draw.

Reinstall each fuse and then check the draw again. If it increases, look for a short in that circuit. A few circuits will have a draw all the time like a clock.

Good luck, be patient.

Good advice. How about first checking the total draw on the battery when the ignition switch is in the off position? Then, it could still be the alternator if it is not charging or charging poorly. That could even drain a new battery after a couple of days with driving. The easiest way to check on the alternator charging decently is to put a volt meter on the battery while driving and it should always read 13.8 Volts. Then the battery is charging.

[pors1968]

Samething window relay defect same as explain JR bennet

[74-911]

This is a good video on tracking down parasitic battery drain:

3 Ways Of Finding The Cause Of Key-Off Battery Drain (Parasitic Draw) - YouTube

[CiscoSF]

Happened to me with an interior light above the radio.

[Nathans_Dad]

I might have a possible solution. I charged the battery enough to crank and started the car. I noticed that the light above the glovebox was on and I discovered a 3 position switch there. I was able to turn the light off and let the car idle for a bit. I turned off the car and with the switch in that position the light was on even with the key in the off position. So, I turned it back off, hoping that it's as simple as that. I'm thinking the wife switched it on by mistake the last time she was in the car.

[porwolf]

Originally Posted by Nathans_Dad

I might have a possible solution. I charged the battery enough to crank and started the car. I noticed that the light above the glovebox was on and I discovered a 3 position switch there. I was able to turn the light off and let the car idle for a bit. I turned off the car and with the switch in that position the light was on even with the key in the off position. So, I turned it back off, hoping that it's as simple as that. I'm thinking the wife switched it on by mistake the last time she was in the car.

Good catch. Reminded me to check that glove compartment switch out on my '79. Just looked up my manual again and here is the description of that switch:

[Nathans_Dad]

Yeah that's the one. The car did turn over when I came home from the movies but it was a weaker crank than when I left a few hours ago. I'm letting it idle again now to charge it back up and I'll try again in the morning. If it's dead in the morning I know it's more than just that light.

[Cooper911SC]

Sounds like you may have found the culprit! Good catch.

All, keep in mind, the alternator is NOT meant to charge a dead battery. It is meant to maintain the battery and help run other electrical systems.
You can damage the alternator trying to charge a completely flat battery.

Better to use a trickle charger to recharge the battery.
Don't forget to check the water level in each cell and top up until the meniscus of the water is at or slightly above the split ring in each cell. Use Distilled water to top up.

Cooper