BMW E31 8-Series - Tracing Battery Drain

Timm's BMW E31 - How To Measure Battery Drain

It’s much more likely you have killed your batteries

The E31 Forums are stuffed with posts regarding ‘battery drain’ - usually along the lines of: The car was working flawlessly, I didn’t drive it for a week and then it wouldn’t start because the batteries were discharged, hardly a click, I think I have battery drain, how do I fix it?

Well, it could be battery drain, but it is very unlikely - but rather than just guess, let's measure it!


Before you can perform an accurate measurement:

•The meter must be capable of measuring 10A and have clamps large enough to get around a battery terminal
•The batteries must be fully charged - the measurements are invalid with low battery voltage
•The batteries must be in good condition - if in doubt buy two new ones, owning an E31 is never cheap
•Make sure the emergency boot operation works just in case you get something wrong:

https://www.meeknet.co.uk/e31/BMW_E31...

As the E31 has two batteries this simplifies the testing, we can leave one of the batteries connected while the meter is fitted to the other battery - this is important as it preserves the evidence that may be lost if the power is completely disconnected as this resets all of the electronics. When the meter is in place the second battery can be disconnected - here’s how to do it.

More information here: http://www.meeknet.co.uk/e31/E31_Batt...

Original music copyright Tim Meek 2018