[twinrink]

Hi
I got M850 and last week i swapped the trunk main battery for new one and registered via bimmerlink.
Driving the car daily for 20 miles and today few days later there is message battery low.
Seems the car is not charging.The small battery in engine bay wasn’t changed.
What can be wrong?
The IBS sensor is bad?
Alternator?

[Hornethandler]

Can you put a voltmeter on the charging posts under the hood and measure the charging voltage?

[twinrink]

Charging voltage with engine on?

[Hornethandler]

Yes. The engine needs to be running for the alternator to supply charging power to the battery. The voltage measured at the jump posts should be between 13/14 volts DC.

[twinrink]

While engine is running it is reading 12.2 Volts
Either alternator or ?

[Tenac]

If there are no devices between your measure points and the alternator its the alternator...

[Hornethandler]

Originally Posted by Tenac

If there are no devices between your measure points and the alternator its the alternator...

Agreed. I suspect there's some sort of protection device (fuse) between the alternator and battery, so I'd start looking there first.

If at all possible, measure directly at the alternator, or at some point (connector) before the battery. In other words, chase the voltage back to the alternator.

[Tenac]

Originally Posted by Hornethandler

Agreed. I suspect there's some sort of protection device (fuse) between the alternator and battery, so I'd start looking there first.

If at all possible, measure directly at the alternator, or at some point (connector) before the battery. In other words, chase the voltage back to the alternator.

The controller that alters the voltage should be in the rear of the car along with the starting battery. So like you said if you can get to either before that where the alt comes in first or the back of the alt would be best.

[twinrink]

I’ll try to measure by alternator but it is difficult to reach.
Other suspicious place would be IBS sending wrong data

[Tenac]

Originally Posted by twinrink

I’ll try to measure by alternator but it is difficult to reach.
Other suspicious place would be IBS sending wrong data

Something you should also try, car not running measure battery voltage. Then start the car measure again it will rise to 13-14v.