Battery Maintenance?

[MWCLS]

Hi, I currently have a Ctek xs3600 battery charger, I only drive my car in good weather, so it won't be getting much use over the next few months.

The car a ( 2006 CLS 350 ) last week had a service B at the main dealer, no advisories! ( car has FMBSH ). Before the car went in for a service I had the charger hooked up on the main boot battery just to keep things tiptop, then I get the dreaded visit workshop battery in red on dash so I get the batteries checked, the Aux is toast not holding charge, I replaced it with a new OEM battery from MB, fixed the problem, I also had the alternator and main batt checked all fine.

Now my worry is am I causing an issue by just keeping the main batt maintained? Do I need to purchase another charger to keep the aux maintained?

Sorry if it's long winded and seems like a silly question, but I can't find any info on the net, I'm slightly OCD with my car so any info would be really appreciated .... Or am I just causing issues doing what I'm doing?

Regards

Michael

 

[Paparazi]

Good charging regime

I can only talk generally and with the assumption that the two batteries remain disconnected from each other whilst laid up.

The Ctek range of chargers are SMART and are designed so that they can be left connected indefinitely without fear of boiling the battery dry. These chargers go to a 'floating state' when they sense the battery is fully charged.
A vehicle left standing for long periods of time without being started will suffer battery drain with eventual battery failure as the flat battery becomes sulphated.
You are taking very sensible precautions by charging the main battery but as you rightly point out, the auxiliary battery also needs the same attention.
I would connect the Ctek to each battery in turn leaving it connected for 2 - 3 days on each one every 4 to 6 weeks.
My only query would be the amount of drain that each of these batteries are being subjected to from ancillaries and if you have noticed a pattern whereby the battery goes flat after a certain period of time.
Nothing to worry about as long as you don't allow batteries to discharge below 50% (12.3 volts ..although this varies)

In short, batteries do not like to be discharged for any length of time and so a good state of charge should be your priority at all times. Over charging can also be just as bad but as you have a SMART charger this is very unlikely to be an issue.

Martin

 

[Rajindran]

Hai there,

I'm a new comer for this forum and appreciate if someone of you guys to help me sort out this problem. My central locking sometimes starts to operate automatically while I'm driving, means its locks all four doors. When the car parked and manually lock the door from the driver side, its locks the other 3 doors and unlocked seems to have no problem. But I could here the sound of motor running and figure out that the vacuum pump underneath the rear seat is working continuously. What will be this cause? Is the vacuum pump motor failure and do I need to replace a new pump? Please advice. Thank you.

 

[Rajindran]

Forgot to tell you guys. I'm driving Mercedes W124 model year 1992.

 

[Dec]

Ragindran, could you start a new thread here… Electronics - MBClub UK - Bringing together Mercedes Enthusiasts
You will see a New Thread button near the top of the page like below.

Dec

 

[grober]

MWCLS I would surmise that the reason your auxilliary battery has gone AWOL is due to old age [ its probably the original factory fit] and the recent drop in ambient temperature. I don't think you have anything to worry about. The onboard electronics should take care of any charging issues so just connect your charger to the main battery in the boot.

The charging is controlled by the BCM [ battery control module] which will direct charge via relay K57/2 to the aux battery if required. Its really a backup battery so under normal circs will have no real drain on it. The CTEK will supply the required charge to the main battery to keep it topped up for any periods of inactivity. Mercedes recommend on these modern setups that cars should not be left inactive for more than about 2 weeks [ maybe that's a bit conservative to be on the safe side ? ]without some form of battery top up.

 

[Ginger55k]

MWCLS I would surmise that the reason your auxilliary battery has gone AWOL is due to old age [ its probably the original factory fit] and the recent drop in ambient temperature. I don't think you have anything to worry about. The onboard electronics should take care of any charging issues so just connect your charger to the main battery in the boot.

The charging is controlled by the BCM [ battery control module] which will direct charge via relay K57/2 to the aux battery if required. Its really a backup battery so under normal circs will have no real drain on it. The CTEK will supply the required charge to the main battery to keep it topped up for any periods of inactivity. Mercedes recommend on these modern setups that cars should not be left inactive for more than about 2 weeks [ maybe that's a bit conservative to be on the safe side ? ]without some form of battery top up.

That's spot on advice, i use the CTEK as well but every now and again connect up to the front battery just to see how its performing, last time i did it it went through all its tests to a floating charge within 2 hours, that gives me the confidence that the front battery is good, I still hook up the rear at least fortnightly on the 55 as its only a weekend toy.

 

[MWCLS]

Thanks guys for all of your advice, you've all been more than helpful. I wasn't sure with the aux, yes it was the original so served the car well. I'll get the ctek hooked back up this evening and alternate between the two just to play on the side of caution.


Although following on from Grober's advice if the batteries "communicate" via the BCM and relay I think for now I will hook up the main battery ( OEM 2 years old ) keeping my eye on things.


Regards



Michael

 

[Paparazi]

How does the BCM work.

MWCLS I would surmise that the reason your auxilliary battery has gone AWOL is due to old age [ its probably the original factory fit] and the recent drop in ambient temperature. I don't think you have anything to worry about. The onboard electronics should take care of any charging issues so just connect your charger to the main battery in the boot.

The charging is controlled by the BCM [ battery control module] which will direct charge via relay K57/2 to the aux battery if required. Its really a backup battery so under normal circs will have no real drain on it. The CTEK will supply the required charge to the main battery to keep it topped up for any periods of inactivity. Mercedes recommend on these modern setups that cars should not be left inactive for more than about 2 weeks [ maybe that's a bit conservative to be on the safe side ? ]without some form of battery top up.

The way you explain it assumes the BCM is active and keeps the auxiliary battery charged up when the vehicle is inactive.
Do you know this for sure? is this unit some kind of battery to battery charger or work like a simple split charger by connecting the two batteries together when the engine runs.
All I am saying is, can you explain how the BCM works when the car is not running, does it pass on charge to the second auxiliary battery under these conditions?

Martin

 

[grober]

The battery in the boot supplies the on-board electrical system in normal operation.
The additional battery is basically a short-time backup for the power supply in the event of the on-board system battery failing.
As I understand it the only way the batteries are normally charged is when the alternator is running. The BCM will sense when the auxilliary battery is low on charge and direct current from the alternator to charge it. When the car is switched off /sitting the auxiliary battery is essentially disconnected by relay k57/2 and would have zero current drain on it so the likelihood of it going flat would be very low. This is not the case with the main battery which still has to power the main car systems alarm etc albeit at a very low level.

quote:-





Sequence of functions:

• The battery control module monitors the operating states as well as the voltage conditions in the vehicle.
• Depending on the performance measured for the battery, consumers can be switched off in 2 priorities (switched off by means of CAN message).
• The battery control module (BCM) also activates the battery isolating relay (K57/2) if necessary. A distinction is made between 2 states:
- recharging of additional battery
- engaging additional battery in critical on-board network situations

If you are asking will the BCM allow the charger to charge the auxiliary battery via its connection to the main battery [OFFLINE=NO ALTERNATOR RUNNING] I'm afraid I don't know the answer to that one. I can only answer by saying if the auxiliary battery is in good nick [ age and therefore charge retention wise] and the main battery is kept charged up then it should never be an issue really.

 

[Paparazi]

With respect...what you are not taking into account is that a fully charged battery will go flat even if there is no current draw made on it.
The original poster is concerned about a flat auxilary battery and the need to charge it when left for long periods.
To me thats a no brainer.....even a fully charged battery will need periodic charging and should not be left more than 10-12 weeks irrespective of discharge.
You only have to look at Caravan leisure batteries to see this trend...where the absolute worst thing you can do is leave the batteries over winter without any charge regime.
Sure, It sounds like the battery needs replacing but I would also recommend a 6 weekly 2 - 3 day charge with that little Ctek.

Martin

 

[Ginger55k]

One of the common faults is battery convenience function disabled which can mean either the front battery is past its sell by date or there is a fault with the BCM, or other issues.

STAR I think would tell you this, that's why in my previous post i connect the CTEK every now and again to carry out a full function test of the front battery.

 

[MWCLS]

Well I've just connected the aux batt in motorcycle charge mode and the light went green within 2 mins, fair enough it's a new battery, the main battery only went green this morning plugged it in at 9pm lastnight and checked it at 6am and it was still charging, by 6.30 it was green.

I haven't driven the car since service on the 5/11 so maybe alternating between the two as suggested by Martin and Ginger 55k is a good idea.

Thanks again everyone for your input, I'm ex BMW driver (M3) please don't hold that against me haha which has a great forum, it's good see this forum is just as informed and helpful.

 

[Ginger55k]

Well I've just connected the aux batt in motorcycle charge mode and the light went green within 2 mins, fair enough it's a new battery, the main battery only went green this morning plugged it in at 9pm lastnight and checked it at 6am and it was still charging, by 6.30 it was green.

I haven't driven the car since service on the 5/11 so maybe alternating between the two as suggested by Martin is a good idea.

Thanks again everyone for your input, I'm ex BMW driver (M3) please don't hold that against me haha which has a great forum, it's good see this forum is just as informed and helpful.

That sounds very much as it should be, i did forget in my original response to mention to select the bike battery mode as this is really what it is.

 

[PhilLockyer]

Hi all,

Just my 2 cents on this. My CL600 is suffering from a number of re-occurring error messages (ABS, ESP, Parking Brake, ABC Suspension etc.). Having had wheel sensors replaced, and the ESP Module (!), the errors unfortunately returned at the weekend.

As the car hardly used, I decided to buy and hook up a good quality ‘smart’ charger to the auxiliary battery. Firstly, I was amazed at the size of the thing - it is bigger than the crank battery in the engine bay!! On the pre-face lifted W216's, it is located in the boot, behind the rear seats. Beware - the panel is a pain to remove! I hooked up a permanent feed using 2 10mm nuts on the existing battery terminals, and plugged in the charger. The charger reported that the battery had less than 25% charge. It took at least 4hrs to charge the first 25%, and has now been on charge for 24 hrs, and isn’t fully charged as yet....

...I am hoping this is the cause of my many intermittent issues – fingers crossed! Obviously, I should have done this as soon as I purchased the car

Cheers,
Phil.