ukcls

Hi. I have a 2005 350CLS which has the message "convenience functions disabled" on startup for about 2 miles. I know it has 2 batteries but the handbook says it has one so how do the 2 work in unison i.e. charging and what is either used for?

teamspb

I believe it's a starter battery. Have you checked the voltage of the car before you start it first thing in the morning?

Inf4life

Funny that I see this because I ran my battery dead the other day and I replaced it with a brand new $200 battery. Now I'm getting the exact same message saying "Low battery convenience features disabled" I'm about to take my care into my shop on Saturday and find out what is wrong because I need my heated seats to work. Plus, it feels like my car is running slightly sluggish as well.

djrabbi

It can be the battery control module? I only get this when it is REALLY cold outside. I haven't changed my battery yet. maybe this weekend?

Any of you guys know what size it is?

ukcls

Yes i think the battery in the boot is getting a bit old but i have been told the starter battery is under the bonnet (hood). I would be grateful if you could tell me if the garage tells you how the system works as i don't seem to get any sense from anyone.

Inf4life

This is what I bought:

http://www.oreillyauto.com/site/c/de...0423&ppt=C0005

Didn't have time to drop it off on Saturday so hopefully I can get it done this week. Still having the same problem with it.

Inf4life

Ok update: I had been getting the same message about my functions being disabled so I'm heading to work yesterday and as soon as I make the turn to get on the highway I get the Battery indicator/Visit Workshop light on my dash. Luckily the road I was on had my shop only about a 1/4 mile down the road. So I pulled up to the shop and turned off the car. Then the Alternator/Battery/Stop Vehicle light came on. Told them what the problem was and they got back to me after lunch. Come to find out my alternator was bad. $675 with parts and labor.

ukcls

Sorry to hear that, a new battery is a lot cheaper! Seems a bit strange though to go straight after you fitted a new battery, don't really know what to make of that. Just a coincidence probably.

teamspb

There are two batteries in the car, the front auxiliary battery and the rear main battery.

The front battery is relay controlled and is only used to turn the engine over (starting the car). In order to test this battery, you need diagnostic software to unlink the two batteries. Only the can you test/charge the battery in the front.

The rear battery is a lot easier ie you just stick a charger on it.

9 times out of 10 it's the aux battery.

If the battery in the rear is the original merc battery, you can have a look around the battery (normally near the terminals) for a date stamped into it. You can then work out how old the battery is and if it is worth while changing it for a new one.

boschk

Get yourself a multimeter and learn how to use it. Testing alternators & batteries is mechanic 101. A decent meter is 40-50 bucks and saves a lot of time and guesswork.

ukcls

I do have a multimeter and know how to use it as i am a time served electrician by trade. What i wanted to know is how the system works so i can fault find. In my car the rear "main" battery is original but everything seems to work ok with the message on. As the car starts well i presume the front/auxillary battery must be newer than the rear. I think it is daft calling the front the auxillary as it starts the car. Calling it auxillary infers that it is not used for the main purpose of the vehicle.

MBtech1098

The auxilary battery on a 211/219 is not a starter battery. The system is completely different then the dual battery setup found on 230, 240, and early 221 chassis.

ukcls

That is my problem. Teamsbp says the front starter is an auxillary whilst you say the auxillary is not a starter (sounds correct to me) but I still don't know how the system works and how can I therefore fault find. Maybe I will try to prise some info from a dealer. My handbook even says it has one battery! Haha.

MBtech1098

The auxilary battery, G1/7 only supplements the main battery G1 in undervoltage situations. This is monitored by the battery control unit N82. When undervoltage is detected consumer shutoff is activated via a message on CAN B and relay K75 which opens circuits 30 and 15R to the cigar lighter and 12V power outlets. At this time relay K57/2 closes and connects G1/7 to the rest of the electrical system by way of fuse box F33.

You'll notice as SBC went away for MY2007 so did this battery system...

ukcls

Ah right i see that makes sense. So i am correct in thinking that ordinarily the rear big battery will start the car if it has the charge but as mine seems to be too old the small front battery is doing the starting and the car loses some features until the rear is charged ok (by the alternator) or the other features are enabled due to the alternator output being sufficient.