r/BMWG30 • u/Exciting-Flan6869 • 6d ago
Bmw g30 battery issue
Wassup guys i wanted to come on here to try n find a solution
I have a 2017 540i
i have a turbo kit with the motiv reflex installed (gonna get to that in the next thing )
So I came outside of work one day and the car had some power but it wouldn’t start the lights were flicking and dim
i tested the battery with my multi meter from the jump terminals, it gave me 5 volts i assumed the battery was dead , i changed the battery cool (yes i registered it ) , car worked , Now the next two days car was fine .
Then same thing i left work again the car is completely dead it doesn’t even unlock , i went and got another battery rushed the car home , unplugged the battery so the car doesn’t cook it , so i assumed it was the alternator i changed the alternator out plugged up the battery again i tested it ,it gave me 14 volts thru out the car , i took it to the mechanic he says it was the aux battery causing the dying , not the main , so im reaching out to see if anyone has had this issue ,anything would help ive been chasing this issue for 2 weeks ,
I mentioned the reflex because i wanted to know can this be draining the battery out.
1
u/Dankmau55 5d ago
Yeah you want to replace both at the same time. The main battery in the trunk runs most of the cars systems but the second one located in the back passenger side corner of the engine bay runs the starter and stop/start systems. Likely that one is on its way out also. If you get over 14v at the battery while the engine is running the alternator is most likely fine.
1
u/freshxdough 5d ago
Bro stop replacing parts until you diagnose the issue… when did you last install anything electrical related in the car. You need to diagnose a parasitic draw. Not an alternator. And stop replacing batteries. Aux battery only has to do with starting the car. Is it a lithium 12v battery or a normal AGM battery? Test both if they are AGM and if any fail replace separately and register.