2002 BMW 525i battery

Tiny
JEFFMGR
  • MEMBER
  • 2002 BMW 525I
  • 6 CYL
  • 2WD
  • MANUAL
  • 66,000 MILES
Hi, twice within 30 days I had to have AAA replace my car battery. The mechanic said that something is causing the battery to drain, he said his tester showed amperage flucuated. He gave me a card to see his 'friend' the mechanic to fix this. Does this sound normal? What could be causing the battery to go bad twice in 30 days?

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Tuesday, October 26th, 2010 AT 2:11 AM

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Tiny
CARADIODOC
  • EXPERT
Hi jeffmgr. Welcome to the forum. You have two different things going on. If something is draining the battery while the car is not being driven, that does not mean the battery is bad, just discharged. A jump-start will get it going, then the battery will recharge while driving. That will take a good 10 - 20 minutes to charge enough to start the engine again, and around an hour or more to fully recharge the battery. You can connect a battery charger too on the lowest setting for about an hour.

The symptoms of a discharged battery are a rapid clicking sound, like loud playing cards in bicycle spokes, when trying to start the engine, dim head lights and dome lights that get dimmer or go out when trying to start the engine, or everything will be completely dead, no lights, no radio, and no remote keyless entry.

If your month-old battery was indeed defective, there isn't much that can cause that except the battery itself. That is very rare today.

You could also have a charging system problem but I would suspect you would have more problems than just once a month. Even a drain on the battery should show up more often than that unless there was something that got left on once. There is a small drain on all car batteries today because of the insane need to hang a computer on every imaginable part of the car. Every one of the dozens of computer modules draws a tiny current for their memory circuits. Most manufacturers state the engine should still start after the car has been sitting unused for three weeks if the battery is in good condition. Testing for an excessive drain has really been complicated now by the use of computers that draw high current for up to a half hour after stopping the engine until they go into "sleep mode".

If you describe the symptoms you're having, I may be able to help determine what's really going on.

Caradiodoc
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Tuesday, October 26th, 2010 AT 2:38 AM
Tiny
DR. HAGERTY
  • MEMBER
The possible failure items are often detectable with a "short test" of the car systems with the proprietary BMW software that most BMW specific repair facilities employ called a GT-1. They can include, but are mot limited to, a faulty final stage control module for the blower fan, a failed or failing general module that does not allow the car to enter "sleep" mode, aftermarket audio installations or security systems.
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Tuesday, October 26th, 2010 AT 3:34 AM

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