It is not 'while under load' that is the problem, but the fact that the aux. battery will not evidently hold a full 12 volts plus
when sitting for or any length of time as in over night.
That is what the cars' system is seeing or 'reading' when the car is first started up when having sat for some time as in overnight.

When you start it up and let it idle even for even a couple of minutes and you have the red warming message,
and then shut if down and then restart it, the aux. battery has then been 'surfaced charged'
just enough that the message will not come on again.
In other words, it must sit for a lengthy time to loose the charge enough to cause the warning to appear.

I read that our alternators 'put-out' 200 amps!



Derrel

 

NEW does not EQUAL GOOD.. New equipment can be BAD.

 

That's what it sounds like to me too. I'm gonna test it again and see what it shows. If it shows weak again, I'm gonna call my dealer and have a nice little talk. I don't think it comes with any sort of guarantee, but it isn't right if I was sold a weak battery that won't even last a year in my car.

 

Good luck on the talk. Be nice those batteries don't get the same warranty as the one in the truck. If he replaces it being under a year old, he is doing you a favor.

 

Push comes to shove, I can replace it for $80 at Walmart/Autozone/Sears based on all the wonderful info in this thread (thanks to everyone, by the way). Not a big deal, but annoying nonetheless.

 

I recently replaced battery in trunk & alternator on '06 e350 w/66,000 miles. Ok, but red message (visit shop) still comes on; so do I need a new aux battery? I've owned dozens of cars for over 50 years and never heard of an AUX battery. Is MB the only car that has the thing. What's it for?

 

Check the voltage on the aux bat under the driver side / under hood cover by the A/C. If you have under 12 volts engine off you need a new aux. My guess is you do need one. Do a search on this site for Aux battery there are many low cost replacments.

 

I think you meant to say on the passenger side under the Cabin air filter.

 

There's no need to rush out and buy a new aux. battery as you know the rest of your charging system is in good shape.
You may have noticed that once you start your car, and let it run for a short while
and shut it off, and then restart it, the red message warning disappears?

That AUX. battery is there to provide current for the SBC braking system as a sort of back up power supply,
but you know your main, the (rear) big battery is in excellent shape, it being brand new.

No need to bother checking your AUX. battery which is located on the passenger side under the hood
beneath the cover that houses the filter for the fresh air system.
That small battery (AUX.) is no doubt bad, but the system will still function properly because current
is passing through it, that current being supplied from the main battery in the trunk.

Get yourself a new AUX. battery and try and find one that is already filled so you won't have to bother filling the
cells yourself which can be messy and after you fill it yourself, it will need to be charged up, another bother.
Read all through these messages above which I found to be most informative and helpful to be sure.

You do not need to disconnect the rear battery, but you must to be careful and not allow the connections in the
front to contact anything metal as the connection coming from the rear will indeed be 'hot' and sparks will fly!

Nothing to it really once you have done it, and as I said, there is plenty of helpful advise above.
Almost any parts supply house will have the proper battery, and you will find that
your car still has the original AUX. battery made in Italy. Note the date on it.
Mine had 44-04 and that is the 44th week in 2004. My CDI was assembled in November 2004.

So have at it and I hope you 'do it yourself' and save some dinero as many of us have done.
Good luck and keep us posted please.

BTW, where did you get your rear battery and how much was it? Did you install it yourself?

Nosey aren't I?

Regards,



DHG

 

Right Pass side. Rock in left hand,, lets check,, no it's the side without the rock.

I bought my Gell Cel battery replacement from Carquest for the main battery around $200 total. Your price may vary and that was 18 months ago.

 

Thanks green e320 dt for you comprehensive answer. The battery was installed by a local mechanic in Martin County, Fl for just under $200. I actually just called him and he never heard of an aux battery in the E350, although he works on many even newer than my 2006. I'm not sure where the fresh air filter system is located, so I will try to find a more qualified mechanic (other than the dealer) to have the battery looked at, since I am up in NY for the summer and perhaps I shouldn't wait. Appreciate everyone's input.

 

Thanks green e320 dt for you comprehensive answer. The battery was installed by a local mechanic in Martin County, Fl for just under $200. I actually just called him and he never heard of an aux battery in the E350, although he works on many even newer than my 2006. I'm not sure where the fresh air filter system is located, so I will try to find a more qualified mechanic (other than the dealer) to have the battery looked at, since I am up in NY for the summer and perhaps I shouldn't wait. Appreciate everyone's input.

 

Just got this message, going to have to replace the battery or batteries. Starting with the Aux battery, I'll check the voltage to make sure that's what it is. Of course this would happen right after I put it up for sale.

 

Just changed my aux battery 20 minutes work. Bought it in Amazon for $65

 

Got the dreaded red battery code yesteday morning. Purchased a new one and added the acid, waited, and then charged for 2 hrs, 13.4v Installed into car and did the procedures, but still have red code when started up. Pos 1 volts read 12.6 , then start up climbed from 13.3 to 13.7 after idling 4 min. Maybe i need to idle/drive the car for longer to get it fully charged to 14.4v?

I did check the rear battery w/car off at 12.8v, but didnt check with car running. Next step is to do so and replace the volt reg on the alternator. Just hope its not the alternator or BCM that is going.

 

Since you're seeing 12.8volts from the rear battery when the car is sitting , and you are reading 13.7 volts at the
front battery after the car is idling for a few minutes, I would seriously doubt if there are any charging problem.

Why not give it a day or two and see if the red message simply goes away all by itself?

You've got nothing to loose by waiting, have you?



DHG

 

You might just need to drive long enough to clear the compter or if you have SBC the front bat. may need replacement.

 

I replaced the front aux last night. I'm thinking i just need to drive it more than just idling for 4 mins to clear the codes?? Hipe that is the case!!! Or better yet, disconnect both neg terminals of both batteries and wait for 30 min or so... This forum has been very helpful/useful in diagnosis the common issues with the W211.

 

I just replaced my alternator yesterday. The rear battery was reading 11.79 w/o the car running and 12.3 while running. Checked all the usual spots..voltage regulator etc. Took it to interstate warehouse to get warranty chek and charge. Definitely the alternator not charging the battery.
Now comes the fun part. MB wanted 1200 for the part and 300 to install it.
I found the Bosch part locally for 250 and installed it in 45 min DIY. Let me tell you how good it felt to A) have saved that much and B) to have saved that much!
Even the local indy shops wanted to charge retail for a rebuilt part. All i have to say is don't be too hasty.

 

Great job but dont' expect the starter to be easy. Have to jack engine, pull motor mounts and exhaust. I just hired mine done on the starter.

 

Dang, I wish I had read this last year. My aux battery cost me $340 from the dealer.

 

Did you check the isolation relay for the AUX battery? Better to check what is wrong before throwing new parts (the new AUX battery probably wasn't a bad idea anyway, not that expensive).

 

No, i didnt check the isolation relay. How do i check that??

Still getting the Read Battery. Started the car up again last night and let it run for 10 minutes. Dash read 13.7 car off and went up to 13.9volts car idling. Rear battery was 12.8 w/ car off and w/car on 14.1. When i turned on the headlights i saw a drop in the dash reading 13.5/6

Tomorrow (depending on how hot/humid it is) i will replace the volt reg that i have on hand. To me looks like the alternator is working and charging both batteries.

 

If I understand right, you did not measure the front battery voltage, only the rear battery? You would probably need a peak-hold MM to check if the car is properly charging the front battery, or diagnose it with Star. I assume the battery voltage is still good when engine is switched off since you charged it before you installed it. You could load the AUX battery too a bit to be able to detect if the car is charging it.

 

Front aux battery w car off 12.6 and w car on 13.3. Which is same as rear battery. Still haven't taken it out on the road yet. Maybe needs to cycle and be driven for 20 min or more ? Since it's too hot here, I will wait when a bit cool to change voltage regular. Both batteries are def being charged when car is running. Culprit is volt reg and if that doesn't clear the battery code will take it to my Indy to figure what is the problem