W211 Aux Battery - AGM? Gel? Conventional?

[E55BOF]

The frost seems to have finally done for my 2004 W211's convenience battery. Time for a new one, but is it worth spending extra for a fancy AGM or Gel battery, or should I just stick with an A2115410001?

 

[andy27168]

Hi,
I am not sure which battery you need, as you have called it Convenience and Auxillary.
The front battery as it is there only for the SBC Brakes then I would replace with a MB Battery.
The rear battery regarding AGM or Lead Acid, I would replace with what MB say but not necessarily with their own battery.
What is fitted at the moment? AGM or Lead Acid?
It isn't unheard of that a car having an AGM from the factory, MB could change to a Lead Acid type when replaced, and as certain aspects of the control of the charging system being software based then putting the wrong battery may not perform as well, hyperthetically that is.

 

[whitenemesis]

I'm sure it's been posted before but just for info..

W211 Dual Battery System

 

[E55BOF]

I get the message 'convenience functions are disabled' on start-up if the car has been standing for more than forty-eight hours. I understood that to mean that the smaller battery under the bonnet was getting tired.

Thanks WhiteNemesis; I'd not seen that before. It doesn't mention my specific message, but it implies that de-activating electrical functions on start-up indicates low charge in the main, System, battery. If that is so, my previous understanding is wrong, and the System battery is failing. I'll try charging it, and see what happens.

 

[C240Sport97]

Thanks WhiteNemesis; I'd not seen that before. It doesn't mention my specific message, but it implies that de-activating electrical functions on start-up indicates low charge in the main, System, battery. If that is so, my previous understanding is wrong, and the System battery is failing. I'll try charging it, and see what happens.

I had your message .. changed main battery, sorted it.

 

[whitenemesis]

Ditto, I just put on charge. The AUX battery is out of circuit until required to support the system battery.

 

[E55BOF]

Thank you, one and all. NOW I understand, Mr, Fawlty...

 

[190]

A thought about the auxiliary battery. If it's mounted in the boot and has no provision for ventilation then I doubt it will be a standard wet lead acid battery. It will be a sealed battery like an AGM.

In terms of chemistry, AGM, Gel and normal wet cell batteries are all lead acid. The only difference is that in AGM and Gel batteries the electrolyte is immobilised which means they are spill proof and don't gas off hydrogen in normal use. That makes them more suitable for mounting in the boot.

 

[E55BOF]

It's under the bonnet, and ventilation is no problem, but there's no provision for a vent pipe, so a wet cell battery wouldn't do.

 

[andy27168]

The Boot fitted battery, the "systems" battery whether AGM or normal lead acid has a breather pipe routed to outside of the car.
AGM Battery does require a vent, but is only open when excessive pressure is present inside the battery.
The battery under the bonnet has always been a lead acid type, but the boot battery has or could of changed from AGM to normal Lead Acid.
The rear battery on my CLS55 has changed, was originally built with a AGM and now it is a normal lead acid, indeed the AGM Battery that was fitted is no longer available.
This could/probably be the case for the E55 as well.
I have the proper EPC, if you PM me your chassis number I could check which one you are supposed to have.

 

[pmcgsmurf]

I replaced the under bonnet battery in the W211 earlier this year as it hadn't been changed before, £55 from Mercedes.

Just yesterday I also replaced the main 70aH battery (8 years old) but opted for a 100aH one, £98 from main Mercedes.

My cars do a lot of very short journeys and in the winter with a poor battery this can be a problem so good to keep an eye on them.

The 6 year old one in the W212 is also being changed today as well.

 

[toolman1954]

Just yesterday I also replaced the main 70aH battery (8 years old) but opted for a 100aH one, £98 from main Mercedes.

I beat yesterday mornings first of the winter season harsh frost by already having the battery out and on charge. After using the heated seats and screen defrost for a couple of days prior, the battery became a bit sluggish for a morning start, so out it came.
Previous owner had told me he had replaced the battery, so it is only 3 /4 years old, but seems I just have a small 74aH, which in a car with so many electronic "toys" seems a bit lacking for winter use, so I want to replace it with 100aH version. I bought a 100aH for my old 300TD from Mercedes Dealer and that was an excellent battery and cheaper than anywhere else.
Main dealers are a bit sparse around here and it would seem Perth is my nearest from here in Leven,Fife, but just wondered where you bought yours from please? .....Thanks.

Steve

 

[Will]

If you are buying a genuine MB battery, check the price at your nearest MB Commercial dealership. Last three batteries I have bought have been sourced there for considerably less for identical parts - about half the cost.

Standard MB 100Ah battery was £60+VAT, £72 all inc.

AGM might have been the spec when new, but as said I have a feeling many have been replaced with regular lead-acid type over the years with no problems. What's fitted in there at the moment, and how old is it?

 

[whitenemesis]

I had a new MB supplied and fitted system battery in the CLS, lasted 18 months before I started getting the consumers off messages. Charging system was checked at the time and BCM flashed with upgraded software. Seems these cars are extremely hard on their batteries. Changing the AUX made no difference.

 

[clk320x]

I get the message 'convenience functions are disabled' on start-up if the car has been standing for more than forty-eight hours. I understood that to mean that the smaller battery under the bonnet was getting tired.

Thanks WhiteNemesis; I'd not seen that before. It doesn't mention my specific message, but it implies that de-activating electrical functions on start-up indicates low charge in the main, System, battery. If that is so, my previous understanding is wrong, and the System battery is failing. I'll try charging it, and see what happens.

Sorry to resurrect an old thread... but what was your solution Dennis?

 

[E55BOF]

The boot battery was fine, but it was the wrong size - 70AH rather than the 100AH it should have been, and well down on the correct CCA too. It must have been fitted by the c**t I bought the car from, because it's only nine months old. I fitted a new battery of the correct rating, and it's fine now.

 

[clk320x]

The boot battery was fine, but it was the wrong size - 70AH rather than the 100AH it should have been, and well down on the correct CCA too. It must have been fitted by the c**t I bought the car from, because it's only nine months old. I fitted a new battery of the correct rating, and it's fine now.

Thanks for that Dennis - much appreciated.