Still haveing Battery Discharge problems, battery randomly goes dead even when charged all night.?

[Ray4256]

I have replace everything bu the alternator and voltage regulator. The meter says the alternator is good , how can I tell if its the regulatro?

[Greydog]

Hi Ray

When my Mercedes had this seemingly random issue alternator output was always good. The discharge became more frequent I put a clamp ammeter on the battery and could see around a 5amp discharge so started unplugging things the discharge stopped when I unplugged the Voltage regulator a new Bosch regulator was around £50 from memory changed it no more problem. When I tested the old Voltage Regulator it had 3 diodes inside and one had failed allowing the drain.

I would start with the regulator if your changing bits as it is much the cheaper part

Dave

[BRR]

I have a 2001 740il with 121,000 miles with the same battery drain problem. Research suggest a Parasitic Drain. OK. I'll just open my wallet and let a repair shop drain it too!

[Greydog]

Morning Bruce

I will assume the Battery is correct and in good condition. You need to spend some time testing "pulling fuses" then check with a multi meter to isolate systems and find the culprit. If you are not able or prepared to do that then you may find out why some say BMW stands for Breaks My Wallet 😆

If your stuck try and find a good Auto Electrician but remember tracing something like this is time consuming and time at an hourly rate adds up, whoever it is doing the work

Dave