hey guys so i was just cleaning my car and to get all the salt stains out i used a wet cloth and scrubbed the stains out. Then i started the car and in the display it said aux battery malfunction! is this something serious ? did i make something wet?

 

How wet did you get the floor under the front passenger seat?

 

Battery icon came on my 2007 ML 350 and parts store showed the battery needed a charge as if something was left on overnight. I charged the battery and had the same thing happen the next day.

After researching this forum, found it could be the aux battery which is located right next to the main battery. One forum thread had nice pictures on how to remove it. Another had a video which showed how to remove the main battery:

https://mbworld.org/forums/m-class-w...50-4matic.html

The aux battery is to the right which is not changed in the video but do a search and find the forum thread with pictures if needed. Easy aux battery bracket removal with a 10mm socket once the main battery is removed.. remove the main battery rear anchor with a 13mm socket and extension (and cable posts removed with the 10mm socket).

Took the aux battery to Batteries Plus and it tested bad there so I bought one for about $22.00. Since I had the main battery out, I took it in for a test also and it showed on the low side of the good range under a load. Since it was going on 8 years old, and it's not easy to change, I replaced it too. Asked and received 10% off since I've seen it cheaper at other places.

Re-installed both and everything works great and he icon is gone. You may need to do a short reprogramming of the window switches if needed. Simply open and close the windows and hold the switch for a few seconds after the window closes all the way. You may need to do that for all windows including the sunroof.

I did notice since all of this my lift-gate stops about 1/2 way up so not sure if that needs to be programmed in some way. It could be a separate issue that coincidentally happened at the same time. Still researching that one..

FYI: The book said the battery icon could also mean the alternator is bad. Simply test that by pushing the top center "R" button above the odometer. First, be on the total odometer page then push the "R" button three times quickly and scroll to the battery voltage. Should read about 12 volts with the engine off, and about 13.8 or so with the engine running. That indicates the alternator is charging the 12 volt battery.

Another tip: In looking up the lift gate problem, came across another battery write up which mentioned that Pep Boys had 35% off the battery through Feb 28th, 2015. The $200 battery becomes $130. A bargain for the needed AGM battery. Of course I saw that after paying $190 yesterday at Batteries Plus.. Buy on line and put in the promo code SECRET35 at checkout, then go to the nearest store and pick it up. Pay there or on line but order on line.

The guy at Batteries Plus was so helpful and offered me the 10% discount so I thought it was good customer service. Even though the identical Bosch battery at Pep Boys was cheaper, I felt I received a good deal. Both have a 4 year free replacement if needed and are AGM made in the USA batteries. Can't go wrong with either one.

In your situation, water probably didn't affect the battery, maybe just the aux went bad right then. I would think a battery from a 2011 ML would still be good but have them both checked..