Battery drain when top down?

doane2u · 09-12-2019, 11:23 AM

If I leave my top down for an hour or less the battery drains and I can't start the car. Any ideas? I don't hear any of the top motors running, there are no dome lights or other lights left on. Battery tested good and alternator is good.

olds350 · 09-12-2019, 04:16 PM

you need to test for a parasitic draw and that's going to involve a slow a tedious process of watching a test meter as you pull out fuses one by one. When you pull the correct fuse, the meter draw will drop. At that point, you'll at least know what circuit to look for...

Edrift · 09-12-2019, 04:53 PM

Sounds concerning. Something could be shorting to ground without blowing the fuse and draining the battery

doane2u · 09-15-2019, 11:43 AM

Okay, I ended up taking it to my BMW mechanic. The top being down was just coincidence, sorry everyone. It turned out it was the battery. The AAA guy had tested the battery and said it was good and the battery indicator was green which supposedly indicates it is good, and the alternator was putting out +14volts, so I assumed it had to be some other problem. My mechanic said they put a new battery in and let it sit all day with the top up and down and there was no problem. So I'm out about $290 for a new battery with the trouble shooting and $35 for two Uber trips to the doctor Wednesday

But, at least it's fixed and I'm actually glad it wasn't some other problem as the system looks really complex.
Thanks everyone for trying to help. Been driving since Wednesday with no problems any more, sitting with the top up or down.

JimD · 09-16-2019, 09:41 AM

Glad it got solved. I hope the load tester I use would have told me the battery was bad. Sometimes there is a weak connection in the battery and the voltage is fine until you load it. Mine looks like this but I think I paid less for it at Harbor Freight:
https://www.amazon.com/Schumacher-BT.../dp/B000AMBOI0. Handy thing to have around occasionally. It briefly puts a 100A load on the battery (using a resister) and you read the voltage on a color coded scale.

doane2u · 09-16-2019, 05:51 PM

I have a 4 amp battery charger/maintainer. I don't drive that much and it's usually short trips. Even the 135i manual warns that this may drain the battery. Is there any harm in leaving a charger/maintainer attached if I haven't been driving for about a week?

MightyMouseTech · 09-16-2019, 06:11 PM

Quote:

Originally Posted by doane2u

I have a 4 amp battery charger/maintainer. I don't drive that much and it's usually short trips. Even the 135i manual warns that this may drain the battery. Is there any harm in leaving a charger/maintainer attached if I haven't been driving for about a week?

I leave my maintainer on for 4-5 months at a time during winter storage. No issues.

09-12-2019, 11:23 AM	#1
doane2u First Lieutenant 91 Rep 341 Posts Drives: 2012 135i M Sport E88 Join Date: Jan 2016 Location: Carmel, CA iTrader: (0)	Battery drain when top down? If I leave my top down for an hour or less the battery drains and I can't start the car. Any ideas? I don't hear any of the top motors running, there are no dome lights or other lights left on. Battery tested good and alternator is good.
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09-12-2019, 04:16 PM	#2
olds350 Needs a long road trip... 347 Rep 527 Posts Drives: '11 e91, '13 e88, '19 golf R Join Date: Jul 2015 Location: NC iTrader: (0)	you need to test for a parasitic draw and that's going to involve a slow a tedious process of watching a test meter as you pull out fuses one by one. When you pull the correct fuse, the meter draw will drop. At that point, you'll at least know what circuit to look for...
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09-12-2019, 04:53 PM	#3
Edrift Private First Class 75 Rep 187 Posts Drives: BMW 135i E88 Join Date: Jun 2019 Location: Melbourne Australia iTrader: (0)	Sounds concerning. Something could be shorting to ground without blowing the fuse and draining the battery
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09-15-2019, 11:43 AM	#4
doane2u First Lieutenant 91 Rep 341 Posts Drives: 2012 135i M Sport E88 Join Date: Jan 2016 Location: Carmel, CA iTrader: (0)	Okay, I ended up taking it to my BMW mechanic. The top being down was just coincidence, sorry everyone. It turned out it was the battery. The AAA guy had tested the battery and said it was good and the battery indicator was green which supposedly indicates it is good, and the alternator was putting out +14volts, so I assumed it had to be some other problem. My mechanic said they put a new battery in and let it sit all day with the top up and down and there was no problem. So I'm out about $290 for a new battery with the trouble shooting and $35 for two Uber trips to the doctor Wednesday But, at least it's fixed and I'm actually glad it wasn't some other problem as the system looks really complex. Thanks everyone for trying to help. Been driving since Wednesday with no problems any more, sitting with the top up or down.
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09-16-2019, 09:41 AM	#5
JimD Brigadier General 368 Rep 3,547 Posts Drives: 128i convertible Join Date: Apr 2009 Location: Lexington, SC iTrader: (0)	Glad it got solved. I hope the load tester I use would have told me the battery was bad. Sometimes there is a weak connection in the battery and the voltage is fine until you load it. Mine looks like this but I think I paid less for it at Harbor Freight: https://www.amazon.com/Schumacher-BT.../dp/B000AMBOI0. Handy thing to have around occasionally. It briefly puts a 100A load on the battery (using a resister) and you read the voltage on a color coded scale. __________________ 128i Convertible, MT, Alpine White, Black Top, Taupe Leatherette, Walnut, Sport Ordered 5/22/09, Completed 6/4/09, At Port 6/9/09, On the Georgia Highway 6/13/09, Ship Arrived Charleston 6/24/09 at 10pm, PCD 7/21/09
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09-16-2019, 05:51 PM	#6
doane2u First Lieutenant 91 Rep 341 Posts Drives: 2012 135i M Sport E88 Join Date: Jan 2016 Location: Carmel, CA iTrader: (0)	I have a 4 amp battery charger/maintainer. I don't drive that much and it's usually short trips. Even the 135i manual warns that this may drain the battery. Is there any harm in leaving a charger/maintainer attached if I haven't been driving for about a week?
	Appreciate 0 Quote