840ci Batteries Always Dead - BMW Forum - BimmerWerkz.com
1,6,7,8 - Series and Mini Cooper General Chat related to models that do not fit into particular categories above. Please try to put your discussion in more appropriate sections. This section does cover the 1 Series, MINI Cooper and 8-Series vehicles: BMW 830i, BMW 840Ci, BMW 850i, BMW 850Ci, BMW 850CSi, M8, Alpina B12, BMW CS Concept and others.

 
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#1 (permalink) Old 02-07-2005, 06:18 PM
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My 840ci 1997, 25,000 miles has had battery problems since I bought car. If it is left for a few days without driving the car will not start without charging. I can't take it on a weekend trip because I am afraid it won't start the next day. I have replaced the batteries too often. They last two years at max. Any suggestions?
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#2 (permalink) Old 02-07-2005, 09:31 PM
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3 days seems a bit excessive. Read my reply to auroax post. In your case I would recommend doing an amperage draw test or having 1 done to make sure you dont have excessive draw.

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#3 (permalink) Old 02-08-2005, 12:39 PM
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Originally posted by Dirty_Tool@Feb 7 2005, 07:31 PM
3 days seems a bit excessive. Read my reply to auroax post. In your case I would recommend doing an amperage draw test or having 1 done to make sure you dont have excessive draw.

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#4 (permalink) Old 02-08-2005, 12:41 PM
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To Dirty_Tool They did a test two other times and said nothing was wrong. What next?
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#5 (permalink) Old 02-08-2005, 01:12 PM
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Im a BMW tech and I agree three day is way too fast if you are sure that both batteries are good and the right size (I think they should be 70ah) and it charging OK then it must be a current draw. When you test current draw on something a an 840 You must test it through both batteries this mean putting am amp meter in between the earth connect for both batteries and its body mount (this is in the left hand side of the boot) and has the two main battery earths bolt to the back panel. With the car all lock the current draw should full to no more than 90milli amps. This may take up to 16 mins because the car electronics shut down gradually.

Hope this helps
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#6 (permalink) Old 02-08-2005, 04:24 PM
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Somebody correct me if I'm wrong but I thought 840 only had 1 battery. 850 definitely has 2 but I think 840 is just 1.

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#7 (permalink) Old 10-15-2006, 06:21 PM
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840 ci csi and i batteries

I hope this helps you out there are 2 batteries in this vehicle one is a main the other is a backup or thats how the service manager told me. Either way I know the 840 series has 2 batteries opposite sides of the trunk. There is a red wire on the passenger side battery that is bolted on it's the hot from the backup battery. The bad part is the bad battery, if you have one, kills the other battery by draining it down. I've been victum of this more than a few times including having a dead car after 2 hours of the car being off. So please have both batteries checked seperatly by checking the main battery with the backup disconnected then checking the backup while it's disconnected. They can check for current drain then off the main line which should be near zero; with my interior lights on it nears an amp with the ignition key on and nothing running it nears 10 amps! so be cautious that it might be a fault somewhere thats not seen. This includes a bad or corroded 60 amp fuse as I found out myself lastnight, the alarm went nutts and woulden't disactivate and after I got the car running I had no interior lights/window control. This car has a lot of electronics anything can malfunction at anytime and the central locking system will start disabling functions with a low battery the alarm receiver is the first thing, I found out windows are the second thing. to check for a bad or corroded 60 amp fuse the fuse is located by following the black wire comming off the main batteries positive post it's bolted on as well just unbolt it; but a word of caution nothing will work so don't close the trunk while cleaning it. Another hint is take out the bottom green relay in the trunks drive side it controls all lights and will eliminate a light remaning on somewhere as the culprit. Best of luck, bonze82.
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#8 (permalink) Old 10-16-2006, 09:00 AM
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Check your cigarette lighter & the flaslight inside the glove compartment. A member on another forum had the same problem and turned out to be the cigarette lighter. It was always hot causing the batteries to drain. He also drove the car once a week....

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