Whats draining my battery?

[danalyse]

After a few days my battery is dead. Charge it up and the same thing happens. I know these kind of problems are tough to trace. Any suggestions as to how to go about it. Any commons sources of this problem.

[E30_fiend]

Top 3:

1. Bad alternator

2. Bad battery

3. Constant draw from unknown electronics(i.e. aftermarket stereo)


check those and if one of those doesnt fix it then get back to us.






Taylor

[jlevie]

Get you hands on an autoranging DMM with at least a 10amp capability. Set it for amps and connect the meter between the battery negative post and the negative cable with the battery fully charged. Normal parasitic draw (doors and trunk closed, ignition off) is 30-60ma. If you see more than than, pull one fuse at a time until you find the offending circuit. Then using the wiring diagrams (http://wedophones.com/BMWManualsLead.htm) trouble shoot that circuit to find the offending component(s).

If you can't find the excessive draw by pulling fuses, remove the leads from the alternator (protect them from shorting to the body or engine). If the draw disappears then, the voltage regulator in the alternator is bad. If that has no affect start looking for improperly installed aftermarket electronics that connect to unswitched power. Improperly installed aftermarket electronics are probably the most common cause of excessive parasitic draw.

If the parasitic draw is normal, reconnect the negative battery cable and start the engine. If the alternator is working properly you should see about 13.5v at idle and it should rise to about 14v at 2500rpm. If you don't see that the alternator isn't working properly. In may cases the cause of that will be the voltage regulator and/or brushes. If the alternator bearings are still good, replacing the regulator is an inexpensive fix.

If none of those tests reveal anything wrong, you may just have a battery with diminished capacity. Repeatedly running a battery flat will reduce its capacity. And if the battery is four or more years old a few full discharge cycles can seriously affect the battery. Most auto parts houses can load test a battery (or an alternator).

[StereoInstaller1]

Top 3:

1. Bad alternator

2. Bad battery

3. Central locking system


check those and if one of those doesnt fix it then get back to us.






Taylor

Fixed