lmsava

I have an older B Class (2009) and the battery warning light came on for the first time. Having a quick look, one of the terminals on the auxiliary battery is corroded. Is this likely to be the cause of the warning light or does that only come on when the alternator fails? I'm concerned about getting the car to a garage, I'm not sure how long the charge will last.

Thanks for any help.

BlackML550

Assuming you haven't changed the auxillary battery, its most likely that after 14 years, it has failed. Whatever it is, have your charging system checked, not just the battery. Good shops will test the alternator as well to make sure its charging. Also, just because a battery shows 12 volts doesn't mean its good. A proper battery tester will put a load on it and tell you if its still good.

In the meantime, clean the corrision off with a wire brush and see if that makes a difference. Unless your main battery is really flat and or dead, if you can start it, you should be able to drive it to get it tested. If you get warning lights especially the esp system, you know your main battery is cooked as well.

BlackML550

How did you go with this?

lmsava

Thanks for your reply, I've been meaning to post again. The battery just had enough left to get to the garage. It turned out it needed a new battery, and the auxiliary alternator belt was split. All seems to be OK now, I'm glad I avoided replacing the alternator