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Car totally dead after a few days unused. Two brand new batteries in last 12 months. The last one only 3 weeks ago. Specialist electrician said was fuse in passenger seat so removed it. Car still went dead after 36 hours. How could this be. He suggests putting kill switch on battery when not in use. Inconvenient. Any suggestions. This is a Z 3 2001. 35000 on clock
 

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Assuming it's getting charged....the way to test for battery drain is to disconnect the positive battery cable and put an ammeter between the battery post and the cable. A digital multimeter is great, just don't try to start it or put any large loads through the meter. It should read in the hundreths of an amp. If it reads in tenths or higher start pulling fuses or relays until the reading drops. That is the circuit causing the load.
Your electrician apparently found something in the passeger seat circuit staying "on" and stopped there.
 

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the bmw altenator is maid to charge the bmw battery. SOMETIMES when an aftermarket battery is installed the bmw altenator doesnt charge the battery properly. it gets confused in a way. this causes the battery to fail, shorten life expectancy, or have a half charged battery. you can take the car to the dealer and they can program the car to run with the batttery installed. or, buy an oem battery. but this is only assuming your not using a oem battery already. a few people say the Z series arent battery sensitive but ive found sometimes the aftermarket battery was the problem. food for thought..
 

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I had the same problem with my 2001 3.0. After disconnecting the negative cable and hooking up a multimeter to read milliamps, I found that the car was drawing .25 ma. After 10 minutes the amp draw went to .04. This was because the computers went to sleep. .04 is within BMW specs. I solved my problem by buying a " Battery Tender" at the local Batties Plus. It puts a trickle charge on the battery for long term storage (2 weeks or more). This isn't the perfect solution to me as my pickup will set 2 months and still start. If anyone has a better fix to the problem, I'd sure like to hear it.
 

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M Mad
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the bmw altenator is maid to charge the bmw battery. SOMETIMES when an aftermarket battery is installed the bmw altenator doesnt charge the battery properly. it gets confused in a way. this causes the battery to fail, shorten life expectancy, or have a half charged battery. you can take the car to the dealer and they can program the car to run with the batttery installed. or, buy an oem battery. but this is only assuming your not using a oem battery already. a few people say the Z series arent battery sensitive but ive found sometimes the aftermarket battery was the problem. food for thought..
HUH????

A battery is a battery, if it is a wet cell battery. An alternator puts out electricity at a given voltage. 13.8 volts in cars. Nothing to program.
 

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YYZED3M Driver
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Amen, Terry...... never heard of a programmable wet cell battery....
Now on second thought... I just might have one for sell.... double the price of a "DUMB" battery.....

Crappy : )

(just outside of Nashville)
 
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