Early W211 conserve battery warning

[timon]

I have tested both battereies and each show 14.1v. Yet on most drives I get a message saying auxiary electrical or luxury items are disabled to conserve battery. What else should I look at?
It's annoying when it's hot to have the a/c blower turned off. Starting has never been a problem.

 

[Blobcat]

Resting voltage should be around 12.6v

14v is charging voltage

 

[timon]

Thanks. but if the charging voltage is correct I assume the alternator is functionning correctly and the car starts every morning normally I assume the battery is holding its charge so what else could be causing the battery protection message?

 

[Blobcat]

If you’ve measured 14.1v you’ve measured it when it’s charging, not the standing state of the battery when everything is off. (Unless your meter is seriously out of calibration)

 

[AMGeed]

As above, measure the voltage with the engine off.
Your battery could be 12v or under yet still start the car and you'd get up to a 14v reading.

When were the batteries last changed?
It's getting more common for some batteries to give up the ghost after 4+ years. My Bosch one did, just 2 months before the guarantee ran out.
They can still show a decent voltage (12.6+), especially after a recharge, but when load tested , the CCA is well below the correct level.

Then its new battery time.

 

[DaveE320CDI]

Whats confusing about W211s with the two battery's is that the small one in the engine bay which is the "auxiliary battery" is used for starting the car! the large battery in the boot the "consumer battery"is for everything else! so when you get that message it means that the consumer battery is on its way out so the car will still start OK on the auxiliary battery as above check the rear consumer battery with engine off and you most likely will find low voltage below 12v, hope this helps and not too confusing

 

[AMGeed]

Whats confusing about W211s with the two battery's is that the small one in the engine bay which is the "auxiliary battery" is used for starting the car! the large battery in the boot the "consumer battery"is for everything else! so when you get that message it means that the consumer battery is on its way out so the car will still start OK on the auxiliary battery as above check the rear consumer battery with engine off and you most likely will find low voltage below 12v, hope this helps and not too confusing

Not sure that is correct Dave. That may be the case with an R230 SL, but not a W/S211
I was always led to believe the main battery in the boot is for starting the car and the auxillary battery under the pollen filter runs the accessories and supplies back up power for the SBC.

The fact the covenience function message keeps getting displayed is often down to the aux battery beginning to fail.
Many 211 owners don't even realise they have 2 batteries.

https://forums.mercedesclub.org.uk/...ience-functions-disabled-which-battery.72304/

 

[DaveE320CDI]

Hi Rodger, Well could be wrong but from experience with mine i got warnings when the main consumer battery was on its way out, and when mine struggled to start after been left for a while it was the auxiliary battery at fault.

 

[Botus]

my fathers does this a lot....

if the batteries are good and you drive once a week you should never see it.
If you just put 25kg of fresh AGM in the boot it won't show up in the first year if you leave for 2 and a half weeks at a time, but in year two, leave for 2 weeks and its on all the time, almost the same as the old one

the incredible bit is the heater/demist fan and the screen wash are disabled for up to 3 miles if the message is on - I can't believe some raving lunatic thought safe driving of a car should be impacted once the engine's running

 

[onefortheroad]

The main battery is for starting the car. You really need a battery conditioner charger to keep it topped up. The w211 seems to be very voltage gready and self protective.

 

[alexanderfoti]

Yes main battery is for starting the car. The small battery in the front is just for the SBC system.

Same on R230's

On W221's with two batteries, the front battery starts the car, the rear battery is for everything else.

 

[Blobcat]

Yes main battery is for starting the car. The small battery in the front is just for the SBC system.

Same on R230's

On W221's with two batteries, the front battery starts the car, the rear battery is for everything else.

With the facelift in 2006 they dropped SBC and I’m fairly sure they only had the one battery after that in a W211. That’s correct isn’t it Alex?

 

[alexanderfoti]

Yup!

 

[LostKiwi]

Yes main battery is for starting the car. The small battery in the front is just for the SBC system.

Same on R230's

On W221's with two batteries, the front battery starts the car, the rear battery is for everything else.

That's not my experience Alex?
On the 230 the front battery starts the car. The rear battery is the consumer battery. With no consumer battery voltage SBC refuses to run (before engine start).

 

[alexanderfoti]

Unless there are two different implementations? I'll need to double check. The 230 V12 I did this week was started and stopped lots with only the rear battery connected.. .

 

[LostKiwi]

Unless there are two different implementations? I'll need to double check. The 230 V12 I did this week was started and stopped lots with only the rear battery connected.. .

Malcolm fitted a charging point to the rear battery as the Command refuses to shut down correctly and keeping the rear battery charged stops consumer battery messages. If I get a consumer battery message (when it's not been on the charger) connecting the charger and restarting the car clears it.

 

[EmilysDad]

I've just seen how much stuff needs removing to access the aux battery on my ML ..... surely a battery change shouldn't be this involved

 

[alexanderfoti]

Malcolm fitted a charging point to the rear battery as the Command refuses to shut down correctly and keeping the rear battery charged stops consumer battery messages. If I get a consumer battery message (when it's not been on the charger) connecting the charger and restarting the car clears it.

You are right, the rear battery can also suplly starter motor after 03 at some point. But otherwise does power the starter normally.