Best way to bring dead battery back to life? - BMW M5 Forum and M6 Forums
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post #1 of 12 Old 13th March 2010, 06:41 PM Thread Starter
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Best way to bring dead battery back to life?

Got an M5 who doesn't want to start. The car was sitting for a month without being touched. I opened the trunk to see that the light was very dim. What is the best way to revive the car? Jump start it, charge it? I've never done this before nor has my buddy. I checked out the manual but I wanted to get opinions from the knowledgable board members
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post #2 of 12 Old 13th March 2010, 06:50 PM Thread Starter
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P.s. I'm not sure but the battery may not be completely dead since the trunk opened and light is hanging by a thread. It also shows some symbols in the instrument cluster such as the battery and seat belt.
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post #3 of 12 Old 13th March 2010, 06:53 PM
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Put the battery on charge using a charger. Leave it for 12 hours or so and then try and start it. If you want it started now then jump it using the terminals under the bonnet and take it for a drive.

Chances are the battery will need replacing but you never know.
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post #4 of 12 Old 13th March 2010, 07:12 PM Thread Starter
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I have the Advanced Battery Charging System that a bought from the dealer two years ago. I never had to use it but how would you do so? Do you hook it under the hood or the trunk? Is this safe for the car? Is charging it fool proof?
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post #5 of 12 Old 13th March 2010, 07:40 PM
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I have two BMWs on trickle chargers all the time ... used them for years. NO problems ... my M5 battery is 7 years old, and still strong. My 323is battery is old and good, as well.

Hook up the batteries to the under hood teminals. Then you can carefully run the power cable, and close the hood and lock it ... Under the hood is much easier than in the trunk.

If you have a LOW battery, charge it slowly for 12 hours, before trying to start. BMWs have a circuit that shuts OFF sensitive electronics (computer modules, for example) when the battery gets TOO LOW.

"The greatest obstacle to discovery is not ignorance; it is the illusion of knowledge."

- Daniel Boorstin
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post #6 of 12 Old 13th March 2010, 08:18 PM Thread Starter
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Thanks! I just hooked it up and it's charging as I speak... Or type I should say So after it's fully charged I should be able to start the car with no problems? Can the battery get over charged?

I feel very silly asking this question but while it's charging can I open the trunk or lock the car?
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post #7 of 12 Old 13th March 2010, 11:30 PM
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Quote:
Originally Posted by bmwluvr4evr View Post
Thanks! I just hooked it up and it's charging as I speak... Or type I should say So after it's fully charged I should be able to start the car with no problems? Can the battery get over charged?

I feel very silly asking this question but while it's charging can I open the trunk or lock the car?
You should have an INTELLIGENT charger ... one that knows when the battery is fully charged, and will then shut off. (Like what is called a trickle charger.) You DO NOT have to fully recharge it, but you must charge it enough to "light the engine off." I DO NOT recommend using a jump start ... too many delicate electrical parts to take a chance. Sure you can jump start it, but DON'T come to me looking for help, if you happen to fry something. (If the car has been charged for an hour, you can try to get it rolling ... downhill ... and, pop the clutch. It may start, but have a place to plug in your charger at the bottom of the hill. if it doesn't.)

Then, and this is important ... drive the car for an hour or so ... unless, it was fully charged on the charger.

You can get in and out of the car with the charger on ... It will just extend the charging time for a minute or two.

UPDATE: And, watch the battery for a couple of months ... make sure it isn't going "south," or that you have a parasitic drain.

"The greatest obstacle to discovery is not ignorance; it is the illusion of knowledge."

- Daniel Boorstin

Last edited by jclyman; 14th March 2010 at 04:38 PM.
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post #8 of 12 Old 14th March 2010, 07:09 AM Thread Starter
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Thank you to the both of you for responding so quickly! I love how the members on this board are very courteous. Compared to other forums I've been, there's no question about it that the M5Board is number 1! That's what keeps me coming back
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post #9 of 12 Old 14th March 2010, 10:03 PM Thread Starter
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Update: looks like the charger is draining the battery instead of helping it. I have another charger that I use for other vehicles. It's DieHard and has three different setting. 50 amp, 10 amp, and 2 amp. The BMW charger is 1.25 amp. Is 2 amp too much for charging it?
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post #10 of 12 Old 14th March 2010, 10:21 PM
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Quote:
Originally Posted by bmwluvr4evr View Post
Update: looks like the charger is draining the battery instead of helping it. I have another charger that I use for other vehicles. It's DieHard and has three different setting. 50 amp, 10 amp, and 2 amp. The BMW charger is 1.25 amp. Is 2 amp too much for charging it?
NO, 2 amp will be fine ... just use the lowest amperage you can. You want to slowly bring the battery back, NOT SHOCK it back.

Old battery chargers CAN drain the battery, if something inside the charger has gone bad. Years ago, I had one that did, as well.

"The greatest obstacle to discovery is not ignorance; it is the illusion of knowledge."

- Daniel Boorstin

Last edited by jclyman; 14th March 2010 at 10:23 PM.
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