Red battery light coming on in higher RPM

[Halftim3]

It turns off when rpm drops back down to normal driving speed around 2-3k rpm.

It gets triggered in the 4-5k rpm.

I'm guessing alternator going bad, but i had it rebuilt in 2022 by a local specialist. It is a Valeo part. I also replaced the tensioner in 2023, about 20k miles ago.

Could it be anything else, maybe a loose belt? Although i checked and it seems tight.

Has anyone had a similar issue to this, how would you diagnose it?

[maw1124]

This is a guess... tensioner. Was the tensioner you put on OE? I've learned the hard way to only use OE (not OEM) tensioners on BMW and Benzes.

I'm interested in others' thoughts as well.

maw

[Halftim3]

INA brand tensioner.

Is there a bearing on the alternator/pulley?

Some more info: when the red light isn't on, the digital charging in the cluster reads 14.4v (at idle, running/driving normally)

Thanks.

[BTB]

This is a guess... tensioner. Was the tensioner you put on OE? I've learned the hard way to only use OE (not OEM) tensioners on BMW and Benzes.

I'm interested in others' thoughts as well.

maw

Can't guarantee OPs issue is tensioner but 100% agreed on OE being mandatory on these. Had a Advance Auto tensioner blow up on me before

[sapote]

INA brand tensioner.

Is there a bearing on the alternator/pulley?

Some more info: when the red light isn't on, the digital charging in the cluster reads 14.4v (at idle, running/driving normally)

Thanks.

It's weird that the BATT light was on with 14.4v charging. You should measure at the batt posts while rev up the engine to 4k; if the batt red light is on, then replace the alternator regulator.