ChuckinTucson

My mother-in-law has a 2006 E320CDI with about 85,000 miles on it. Lately she is getting a message saying that the battery voltage is low and convenience features are shutting off. At this point, the A/C shuts off.

I read the forums a few times and it seemed the logical place to start was the battery under the hood, which was replaced this afternoon. Unfortunately this didn't solve the problem.

Is my next step to replace the battery in the truck or get the BCM flashed? Any input would be helpful.

BTW, it is just a regular message, nothing in red like a huge warning type message.

Thanks!

N_Jay

Have the batteries tested.


My guess is the main battery (trunk) is going bad.

rmart73

I would check the aux battery in the engine compartment, its on the passenger side near the firewall, same box as the cabin filters. I have on 03 w211 (gas) and thats where mine is.

N_Jay

EXCEPT here said he replaced that battery.

ChuckinTucson

Replaced it this afternoon (see original post). Problem persists.

ChuckinTucson

This was going to be my next step. This battery is obviously the one that starts the car and it does that with no problems. The msg and problem starts once the cars been driving for awhile, which leads me to think that it isn't the battery, although it wouldn't hurt to get it checked. That will be next on my list.

rmart73

Yeah...missed that part. So I found this from Keyhole at Benzworld "Info from my WIS:

The 2 battery power supply is a complex system. It comprises the main battery (G1) in the trunk, the auxillary battery (G1/7) in the engine compartment, the battery control unit (N82), and the auxillary battery relay (K57/2).

If a problem is sensed by N82 in any of the above items (plus the alternator) it is able to reduce power to selected consumers in two stages, 1 and 2. Cut-out stage 1 is when G1 voltage is below 11.0v dc, and cut-out stage 2 is when G1 voltage is below 10.5v dc. Normally it will be about 14.2v dc when the Alternator & VR are working OK.

The warning message (in white at the cluster) seen by the OP was given because: "The charge level of battery G1 is too low". In that particular case I would have suspected either the alternator or the voltage regulator.

MB can fault find the 2 battery control system with their STAR DIAGNOSTIC."

http://www.benzworld.org/forums/w211...available.html

If its not the batteries then I would guess the Battery Control Unit.

ChuckinTucson

Thank you. I'm not at home at the moment, but I'm going to have her take it to AutoZone and have them test the battery. Hopefully they can do it while it's in the car. If it's okay, we'll take it to an indy MB place here in town and have them check it out. Was trying to narrow it down without having to take it into the shop.

Thank you everyone who responded. I'll post when we've found a solution.

cetialpha5

If the battery checks out, my guess would be the voltage regulator. There's several threads on here about how they do tend to wear out. I hate to throw parts at a problem, but even if it's not the regulator, it's probably about time it needs to be replaced anyway.

josh8loop

Make sure to get an AGM battery for it like Exide FP-AGML5/49

I replaced my main battery in the trunk after I had the battery message you listed and was noticing slight voltage fluctuations. The previous battery was the original battery and it was 9 years old so I figured better to do it now proactively than to have the wife stranded somewhere. So far it is working fine and is the exact form fit and funciton down to the vent tube location. I ended up getting mine from:

http://www.batteryservice.com/produc...=FP-AGML5%2f49


Hopefully they still have it in stock and available for a reasonable price. They were absolutely the cheapest price out there by quite a bit when I bought from them.

I would start with the main battery first, and then if needed move onto the voltage regulator of alternator replacement. 90K miles isn't much for an alternator so I bet your issue is the main battery. Only thing I had to do after the replacement was to reinitialize the windows, sunroof etc. Nothing major at all. Owners manual covers all of that.

cetialpha5

I think that site has them for $182. There's a lot of options if you want to get one locally. For instance, Autozone has their Platnium H8 AGM battery for $180 but they have a 20% discount code so it's $144 after the code. Advance Auto carries it for $190, but they have a 30% off code with a max discount of $50 that brings it down to $140. And Pepboys has a Bosch for $200, but they also have a 25% off code which brings it down to $150. Mail order isn't always the cheapest these days. Those are all AGM batteries. If you just want flooded, Walmart sells one for $123.

ChuckinTucson

Thank you everyone for your input. She sent me this picture today of her dashboard. Not sure if she's gotten the battery checked yet. I'm traveling at the moment (or I should say, as usual) and not at home or I'd do it myself.