View Full Version : e34 battery drainage problem

09-23-2008, 11:42 PM
hey, i have a problem with the e34. i got a new battery in and it just drains over night, i leave nothing on....

how and where should i start diagnosing this problem?

09-24-2008, 08:57 AM
Place a voltage meter on the battery with the engine shut off.
Voltage should read 12.? volts depending the condition of your battery. Your volatge reading will depending on what is draining your battery.

Start pulling fuses, if the voltage jumps you found your problem.
Don't be confused between the systems that are on all the time as normal vehicle operation.

09-24-2008, 11:49 AM
a common issue on e39 is the final stage unit (FSU) remains on after the car is off, i don't know if this applies to e34. but its worth looking into it. quick remedy is to pull off the A/C unit or cliemet control fuse and see the issue goes away.

09-24-2008, 03:33 PM
thanks guys, ill update u soon,

10-05-2008, 08:32 AM
The standard procedure here is to disconnect the charged battery at the negative terminal and connect a meter measuring current between the negative battery post and the wire. An E34 should have @ 20 to 40 milliamps current under normal conditions. You will likely have 200 or more milliamps showing on the meter. To find your current drain, pull relays and fuses until the current drops to the 20 - 40 level. The one that causes the big drop is your culprit.

On a related note has your charging system been checked. With the car running you should measure 14V or more at the battery. Your alternator may be toasted. Commonly when a battery dies it drags the alternator with it (and vice versa). I have also had bad batteries right out of the box. Any garage will be able to load test it. Car batteries do not like being drained down (deep cycled) too many times before the sulfates build up and kill them.