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I've been having an intermitten total battery draining. Battery has been full dead after 24 hours, but not always. I recharged it yesterday and listened for anything that might be running. Next to the battery I could hear a noise coming from the alarm horn. I disconnected the leads from the alarm horn and tested a current of 9.5 volts at the leads. The alarm was not activated (ie. doors not locked, alarm not on). The battery tested at 12.4 volts.

The car is a '01 996 which I recently acquired. The battery is brand new Duralast and is correct for this car.

any thoughts?


Oh, one other things. I reported the problem to my deaaler and they said that I should not leave the car in gear (manual trans) when I park it because there is a gear indicator in the trans that will draw power even with key off. Does not sound reasonable to me.

Edited by Rickster2
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  • Admin

There are several threads here (do a search) for battery drains.

If you put a DC amp meter in series with the battery the draw should be around 40 ma or less.

If not then start eliminating things like the front trunk light still on with the trunk closed, etc. You can also pull fuses one at a time until your draw drops to help pinpoint the problem.

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Oh, one other things. I reported the problem to my deaaler and they said that I should not leave the car in gear (manual trans) when I park it because there is a gear indicator in the trans that will draw power even with key off. Does not sound reasonable to me.

I leave my 03 in gear all the time and sometimes weeks without a charge with no problem

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I attached the photo showing what I believe is my "batttery drainer." I think this is the alram horn??? With key out of ignition and alarm NOT activated this little part was making a humming noise (see arrow). I disconnected the leads and it tested at 9.5 volts.

I left it diconnected overnight and my battery maintained it charge.

Is this part associated with the alarm?

Why is the lead wires putting out 9.5 volts to it?

Remeber, my problem has been intermitten.



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  • 2 weeks later...


You are a GOD. Seriously man. My brother's Boxster had a constant battery drain for years. They just kept it on the Porsche Battery Maintainer all the time. This treated the symptoms, but sure didn't cure the problem.

After reading your post here, I disconected the stupid alarm horn beside the battery and for the first time in 3 years, they can leave the car without the charger attached! It's been a week now without the charger and before it would have been completely dead in two days. We're going to let it go another week before calling this done but I'm pretty sure you solved this annoying and nagging problem for us.

Thank you SO MUCH!


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  • 11 months later...

I'm having a similar problem with contant battery draining after a week, even with the battery maintainer hooked up. It shows constant charging of the battery. I've decided to swap out the battery with my 3 series bimmer's Interstate battery ... surprising, they share the same battery type ... Interstate MTP-91 or group 48. I have the Exide on the Porsche. The Exide performed well on the bimmer .. great cranking, no draining, etc.. Installed the Interstate on the Porsche ...same problem ... battery draining .. even with maintainer hooked up.... doesn't even go into float mode.

I listened to the alarm horn and could hear humming even without activating the alarm. I disconnected the horn and left the battery maintainer connected. I checked the charger the following day and it is in floating mode ... this is great advancement!! I will look into replacing the horn ... and I believe this is the fix to my problem. Thanks

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Darn, local Porsche dealership doesn't have the horn in stock and may take a few weeks to get it. Surprisingly, its reasonable ... $16.40. I went to a local VW dealership hoping to find a similar part. Spoke to the Parts manager, he tested the horn and it works fine. He stated the horn looks like one from an older VW. Unfortuantely he doesn't have one in stock and he couldn't reference the Pcar horn part #.

I explained the humming noise to him, he consulted with his mechanic, and they stated that it could possibly be a wiring or short somewhere causing the hum as they felt there shouldn't be any current flowing to the horn when the alarm is not activated.

Saw the url linking to another discussion on the binker and alarm. It seems that there is constant current flowing to the horn as tested by Toolpants. I guess for $16.40, I'm willing to take the chance and purchase a replacement and cross my finger that this will fix my battery drain problem.

Edited by rlim
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Your wasting your $16.40, because a horn does not activate itself, either there is current running thru it or not. It in itself will not cause your problem. Your horn is triggered else where. You need the schematics to back thru it. Sorry no easy answwer.

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  • 6 years later...

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