[Bristol jake]

Hi guys. I have a 320d e91. battery dies in last cold spell. i replaced it with like for like, but didnt bother have computer synched with battery. i know this may reduce life my a bit, but nothing major as far as I understand.
Whats happening now is that the battery is draining super fast when driving. ONLY WHEN DRIVING. parked up, seems fine. but when I drive the battery will drian down to under 11v in a matter of 30 minutes. Im presuming that i damaged the battery distribution unit when changing battery. does anyone have any experience with this ?
Thanks in advance

 

[Evog]

Sounds like the alternator has failed...

 

[Bristol jake]

The drain seems too fast for it to just be alternator. i thought maybe i had blown something in the distributor that was both draining, and not allowing alternator to charge at same time. is this possible ? seems mad coincidental that it happened sgtraight after i removed the distribution board to change battery.

 

[Evog]

My money's on the alternator - the current draw is absolutely monster when cold - glow plugs, electric aux coolant heater, lights, plus all the electrics to run the engine. There's probably a steady state 50-60 amp call when running. Plus the big call to start it.

Check the charging voltage is the first thing to do. If it's up 14 or more, the alternator's ok.

I did have an aux electric heater start acting up on my E46 330d and that effectively caused a driving drain - so it's possible, but to out run a 120 amp alternator you're talking something with some serious pull!

 

[iamthewalrus]

Do what Evog suggests check voltage when running,

 

[Alan G]

+1 on alternator.
Had that same problem years ago but on a VW.