Mercedes CLS55 Battery questions

[andy27168]

Hi,
I am thinking of replacing the boot mounted battery in my CLS55, apparently my car originally had a AGM battery fitted from the factory and now has a lead acid.
Mercedes and the official EPC state that it should now be a lead acid.
Can anyone think why Mercedes changed it?
Whether changing it back to an AGM would cause me any issues?
Just thinking that the AGM battery would be more resilient to the loads on the CLS, and won't cause the de-activation of the convenience functions lees often (will still start after six days with convenience de-activation).
Though the battery currently fitted is a BOSCH and is OK I need a new battery for my C230K which just happens to be the same size as the CLS.

 

[c63chris]

Be one to check out carefully. On the SL there is a control module which sits between both batteries and can power he car depending on the state of them also monitors battery voltage to determine this. I think an AGM can/should charge at a higher voltage. Originally they said AGM as sealed no maintenance unit though it still needs to vent outside the boot.


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[andy27168]

Hi,
Well that's part of the reason why I am asking, as I have monitored 14.5 volts at the battery with the engine running. Also with 14.5 Volts charging I can see it shortening the life of my current lead acid battery
The module you are talking about I believe can be updated and my car has had all the updates and all software has been updated.
I still find it strange that the standard battery has changed from an AGM to a Lead Acid, I have even tried to buy the standard AGM Battery my car came with from the factory but it is no longer a current pt. no. and no longer available.

 

[Will]

FWIW, I fitted a regular 100Ah genuine MB battery (lead-acid) to my W211 over a year ago and it's been absolutely fine. Can't remember the last time I saw the convenience functions message, always starts well and often sits for several days at a time

It was £62+VAT btw - not sure on the price of the AGM batteries if still available but seemed like good value to me for a genuine battery.

 

[whitenemesis]

I had MB fit a new battery, lead acid type. Fine for 18 months then warnings again. Just the nature of the beast, the CLS eats batteries...

 

[donshl]

I recently got a battery from Mercedes for the CLS and it's AGM one

 

[Will]

I recently got a battery from Mercedes for the CLS and it's AGM one

How much was that out of interest

 

[andy27168]

I recently got a battery from Mercedes for the CLS and it's AGM one

Hi,
There was a chassis break point from which point AGM Battery was replaced by the lead acid.
I enquired regarding the original factory fitted AGM Battery and asked for one of those by Pt. No. and was told it was no longer available.
Would be interesting to see your chassis number on the EPC and confirm.
What MY is yours? mine is a 2006 model but registered very late December 2005.
I have now bought an AGM Battery, a Varta for £143 delivered.
(Varta I believe is OEM to MB, and make Batteries for Bosch too.

 

[190]

Hi,
Well that's part of the reason why I am asking, as I have monitored 14.5 volts at the battery with the engine running. Also with 14.5 Volts charging I can see it shortening the life of my current lead acid battery.....

I've run wet cell batteries at a 14.5 volts and it didn't seem to do any harm as the battery lasted 10 years but it did need frequent topping up.

Does your car have a fixed charging voltage or is it an ECU controlled charger. I came across this the other day which gives an insight in how complex they can be:


The control module enters Charge Mode whenever one of the following conditions is met:


Under WOT conditions and when the fuel rate (sent by the ECM/PCM) is greater than 21 g/S and the throttle position is greater than 90%.
The headlamps are on, low or high beam.
The wipers are on for more than 8 seconds.
The electric cooling fans are on high speed.
The rear defogger is on.
The battery SOC is less than 80%.
When one of these conditions is met, the control module ramps up the voltage slowly to a level between 13.4 to 15.5V (depending upon the mode of operation the system is presently in) at a rate of 8mV to 50mV per second.

The control module enters Fuel Economy Mode when the following conditions are met:

The calculated ambient air temperature is above 32°F.
The calculated battery current is less than 15A and greater than –8A.
The battery SOC is greater than 80%.
The generator field duty cycle is less than 99%.
This mode’s targeted generator output voltage is 13.0V. The control module will exit this mode once the criteria are met for Charge Mode.

The control module will enter Voltage Reduction Mode when the following conditions are met:

The calculated ambient air temperature is above 32°F.
The calculated battery current is less than 2A and greater than –7A.
The generator field duty cycle is less than 99%.
This mode’s targeted generator output voltage is 12.9V. The control module will exit this mode once the criteria are met for Charge Mode.

After the engine has started, the control module sets a targeted generator output voltage of 14.5V for 30 seconds (Start Up Mode).

The control module enters Battery Sulfation Mode when the battery voltage is less than 13.2V for 45 minutes. Once in this mode, the generator battery control module will set a targeted output voltage between 13.9 and 15.5V for five minutes. The control module will then determine which mode to enter depending on voltage requirements.

In RVC Mode, the control module bases the charging voltage on battery SOC, which is estimated during a key-off event every eight hours, after three voltage measurements every 24 hours thereafter, and then monitored constantly while the ignition is on. These voltage measurements are then compared to estimated battery temperature, as battery temperature vs. battery voltage directly corresponds to battery SOC. While the engine is running, the system uses both the battery voltage and estimated battery temperature to determine the battery current in and out of the battery. The control module then regulates the charging voltage to keep the battery above an 80% SOC.

 

[donshl]

How much was that out of interest

I think it was around 180 pounds.

Hi,
There was a chassis break point from which point AGM Battery was replaced by the lead acid.
I enquired regarding the original factory fitted AGM Battery and asked for one of those by Pt. No. and was told it was no longer available.
Would be interesting to see your chassis number on the EPC and confirm.
What MY is yours? mine is a 2006 model but registered very late December 2005.
I have now bought an AGM Battery, a Varta for £143 delivered.
(Varta I believe is OEM to MB, and make Batteries for Bosch too.

Mine was registered in Nov 2005,
VIN: WDD2193762A051736

 

[AlanD]

Question on battery care .. how much of a difference does it really make when connecting both terminals to charge a car vs. chassis earth + terminal? Is it more relevant when you're hooking up jump leads and the potential for spark compared to a "dead" charge lead prior to connecting to the charger and turning the power on?

My charger comes with a lead you can permanently connect to both terminals so that you can just snap-on to charge with the lead's connector to the charger. It would be a lot more convenient than using the clips .. especially as the CLS boot doesn't offer a great deal of earth to clip onto (I use a tiny bolt stem under the foam cover behind the seats)!

 

[Will]

Question on battery care .. how much of a difference does it really make when connecting both terminals to charge a car vs. chassis earth + terminal? Is it more relevant when you're hooking up jump leads and the potential for spark compared to a "dead" charge lead prior to connecting to the charger and turning the power on?

My charger comes with a lead you can permanently connect to both terminals so that you can just snap-on to charge with the lead's connector to the charger. It would be a lot more convenient than using the clips .. especially as the CLS boot doesn't offer a great deal of earth to clip onto (I use a tiny bolt stem under the foam cover behind the seats)!

No need to connect a battery charger to chassis earth, why would you want to? You're charging the battery not trying to jump start the car

 

[whitenemesis]

Except for the W219 dual battery system WIS states to connect the charger across the BCM, using it's body mounting bolt and the battery positive terminal...

 

[AlanD]

Charger instructions clearly state to do so (chassis earth) as step 2 after connecting red if battery is in the car!

That aside, I am interested in any actual science behind it. For example, does it have any bearing on any temporary surge when hooking up? I'm sure I read somewhere about someone speculating on current through sensitive attached equipment .. or maybe that was just if stuff was turned on when you started charging ..!

 

[whitenemesis]

My CLS had the convenience connection installed by MB. I simply plugged the CTEK into that connection. There won't be any surge as one should only connect the charger to the mains once connected to the car battery.

 

[Will]

Chassis earth is directly connected to battery negative terminal, which is directly connected to BCM mounting bolt. If you're charging the battery with a only a few amps from a battery charger I can't see this causing any issue either way.

Earth strap from battery is significantly larger than the charging cables fitted to most battery chargers I have seen.

What does WIS say the reason for connecting in this way is?

 

[whitenemesis]

WIS doesn't explain further than to say the BCM needs to know the car is being charged. I have no idea how this can work...

"Connect positive pole of battery charger
to positive pole of battery. Connect the
negative terminal of the charger to body
ground (2) only (not to the battery
negative terminal) so that the battery
control unit (N82) (up to 31.5.06) or battery
sensor (as of 1.6.06) can detect charging of
the battery."

 

[AlanD]

Mine's the off-the-shelf CTEK so quite possible the same model and I assume it comes with that kit for a reason (convenience!). It does seem that something well connected permanently is less accident prone than using clips all the time.

Just curious as to why the advice is always to earth when the battery is in-situ rather than use clips on both terminals

 

[Lenny63]

so what battery did you buy in the end Andy?

Strangely I have my ctek wired into the pos & neg terminals of the battery via the quick release connection - My current battery throws a red light on the charger when it reaches step 5 on the Ctek - manual states my batt is not holding a charge properly

Looks like I may need one too

 

[c63chris]

I have my CTEK connected across the boot battery in my SL. Just connected the CTEK plug to the terminals. Car had been iffy if parked up for any period with all sorts of random electronic things happening but now rock solid.


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