Bought the car at 6pm, broken down in a lay by 30 mins later CL63AMG

[growla666]

It went down to around 11.9-12.2 I think then steadied at 12v. So should I replace the AGM battery?

 

[John Laidlaw]

It went down to around 11.9-12.2 I think then steadied at 12v. So should I replace the AGM battery?

Yeah its on the way out, try MB Grangemouth got good prices....

 

[LostKiwi]

It went down to around 11.9-12.2 I think then steadied at 12v. So should I replace the AGM battery?

To do this properly charge the battery fully and measure the voltage (with no circuits connected).
Leave it disconnected 12 hours and measure the voltage again.
If either reading is under 12.4v the battery is toast.
At 12.3 v battery plates will begin to sulfate and rapidly degrade.

 

[growla666]

Which battery is toast the one in the engine bay (wet battery) or the AGM one in the boot which is a gel type? How much are they?

 

[LostKiwi]

Which battery is toast the one in the engine bay (wet battery) or the AGM one in the boot which is a gel type? How much are they?

Whichever one is reading low is toast. Personally I'd change both (but given your situation try and see if you can borrow a couple of batteries first).
Below 12v the electronics start to shut down so if you had 11.9v its not surprising it played up. Then once it managed to get a little more charge it started coming back to life.

The other thing is cars on car yards have a bad habit of batteries going flat (ever noticed they all seem to have booster packs?)... Once a battery drops below a certain voltage they are pretty guaranteed to be dead afterwards.

 

[growla666]

Thanks Lost Kiwi - that's my sense too - thing is I want it to be that the batteries are bad. The car has been sat around and only done 800 miles in the last year so I suspect the batteries are not in brilliant shape. Shouldn't try indy have put a battery tester on them both? And if he did wouldn't they have detected it?

 

[growla666]

Hang on should the alternator charge the AGM battery whilst driving?

 

[LostKiwi]

Thanks Lost Kiwi - that's my sense too - thing is I want it to be that the batteries are bad. The car has been sat around and only done 800 miles in the last year so I suspect the batteries are not in brilliant shape. Shouldn't try indy have put a battery tester on them both? And if he did wouldn't they have detected it?

I would have thought they would try a battery tester but as I wasn't there I can't comment.
If its done that few miles then I would be surprised if the batteries weren't toast. They will almost certainly have been fully flat at some point in that time unless the PO was conscientious enough to keep it on charge all the time.

 

[Submariner1]

Hang on should the alternator charge the AGM battery whilst driving?

Yes but not a lot. Mine did. But 40 mins charging 14.4V to 14.6V Was not enough to allow the car to restart mid way on the STAR quicktest. Mobilo had to hook up some massive cables and restart the test. (With a huge surge protector thingy).
This was on the new crap battery not the final good new battery.

 

[Submariner1]

It went down to around 11.9-12.2 I think then steadied at 12v. So should I replace the AGM battery?

The defective new battery was completely screwing up my car with 11.9V, even with the car started with his help, very big cables (he assured me was not the harmful massive booster ones) and it running at 14.4V thanks to his words "a really good alternator" the car was nuts! And failed 5 pages of STAR diagnostics!

I dont want to get your hopes up ... but all this crazy stuff you are seeing is so so so similar to all the problems I and the mobilo technician had (btw he was a really good proper MB trained workshop technician .. knew every question I asked)
Out of 5 pages of failed test, he instantly picked one item and said ... I can see you don't look happy; but thats the only one that worries me, and its just a broken wing mirror heater. When I come back with a decent battery, you watch I bet thats the only one still there after I clear them down.

Hmmmm I was feeling freeking depressed, seeing that printer churn out page after page of failed test. Yes I admit it, I was somewhat cynical.

But he was right!

If you say your battery was down at 11.9V And had been left pretty much unused formsome time, I really do think if you had 2 fully charged new batteries on there ... my gut feel is all your problems will go away!

One thing that guy said was ... "these big V8s with all these toys do not like poor power supplies ... plays havoc with its systems."

I cant help you which one is the problem, as mine now only has one battery, and having had 4 SL 500s with 2 batteries I know they are fussy.

Could you get the Dealer to spring for 2 batteries ?

OK I know sod all about cars, but have just been through this nightmare.
What confuses me is if the batttery is weak / defective, but we get her started; and having a good alternator, that chucks out 14.2V why dont all the problems go away? ... as surely then the car then has all the volts it needs ??

But it doesnt seem to follow that logic, if the battery is defective maybe the Battery control module gets screwed up.

All I know is put a fully charged new battery on there and see 12.7 or 12.8V (engine off) and everything works perfectly. (14.2V to 14.4V at tickover).

 

[LostKiwi]

I suspect this what may be happening:

With two batteries you have what's called a split charge system (common on boats and caravans).
When the car starts the alternator charge will go to the starter battery first as thats deemed the more important one. Only once the starter battery has reached a certain level will charge go to the second battery. If the starter battery has difficulty charging the second battery will progressively become weaker and weaker as it never gets a full charge. Over time a failing first battery can also degrade a second battery.

I don't know how the systems are connected in this car but I would normally expect critical systems to run from the first battery and non critical systems from the second. Critical systems would be any system required to start the engine the theory being that in normal circumstances once the engine is started the alternator will provide sufficient power (after a few minures) to bring secondary systems on line. If the gearbox ecu is on the secondary battery (it's not required to start the engine after all) but the starter battery never reaches full charge it may explain your symptoms.

 

[growla666]

Back to the garage this morning. They said they did battery tests of both batteries and put them on full over 36 hours so they considered the likelihood it was a battery problem to be discounted. They've got the car back and will no doubt shove STAR back on it to see what faults there are. They said I could replace the battery to remove that fault path once and for all but it was going to set me back £200+ for a new one. They also strongly recommended using OEM only which I probably will do. Confidence in this car slowly sinking.....

 

[growla666]

I suspect this what may be happening:

With two batteries you have what's called a split charge system (common on boats and caravans).
When the car starts the alternator charge will go to the starter battery first as thats deemed the more important one. Only once the starter battery has reached a certain level will charge go to the second battery. If the starter battery has difficulty charging the second battery will progressively become weaker and weaker as it never gets a full charge. Over time a failing first battery can also degrade a second battery.

I don't know how the systems are connected in this car but I would normally expect critical systems to run from the first battery and non critical systems from the second. Critical systems would be any system required to start the engine the theory being that in normal circumstances once the engine is started the alternator will provide sufficient power (after a few minures) to bring secondary systems on line. If the gearbox ecu is on the secondary battery (it's not required to start the engine after all) but the starter battery never reaches full charge it may explain your symptoms.

This sounds entirely plausible - submariner reports similar issues with his car which were resolved by replacing the battery. I could replace both and then that could solve all the issues right? Lot of dosh it it doesn't and I decide to take car back to dealers and ask for a refund under sales of goods act.

 

[JBell]

This sounds entirely plausible - submariner reports similar issues with his car which were resolved by replacing the battery. I could replace both and then that could solve all the issues right? Lot of dosh it it doesn't and I decide to take car back to dealers and ask for a refund under sales of goods act.

Sent the dealer the bill for the batteries

 

[LostKiwi]

This sounds entirely plausible - submariner reports similar issues with his car which were resolved by replacing the battery. I could replace both and then that could solve all the issues right? Lot of dosh it it doesn't and I decide to take car back to dealers and ask for a refund under sales of goods act.

See if you can borrow a couple of known good batteries from the indy.

I would definitely be taking the batteries out, measuring present voltage, charging them fully, measuring voltage and then leaving 12 hours to measure voltages again. If either of the last two readings are under 12.4v bin them.
If the first reading is under 12.4v you need to find why they are discharged.

 

[SL63 Mark]

Now we know the age of the car, 10 year old batteries are likely duff.

Why not just replace the consumer battery ? I replaced mine years ago, £100 all in from MB.

 

[Submariner1]

Back to the garage this morning. They said they did battery tests of both batteries and put them on full over 36 hours so they considered the likelihood it was a battery problem to be discounted. They've got the car back and will no doubt shove STAR back on it to see what faults there are. They said I could replace the battery to remove that fault path once and for all but it was going to set me back £200+ for a new one. They also strongly recommended using OEM only which I probably will do. Confidence in this car slowly sinking.....

Grangemouth are selling 95AH now downrated to 92AH 850cc MB AGM Batteries for £110. (Pretty certain mine is also used on a 2009 CL 63.)
So when you say £200 a battery that sounds veryexpensive. Or was it for both batteries?

Plus as LK said you have the 2 battery complexity.
My SL500 had 2 batteries, this split charging system sounded so complex I even got the supplying dealer to fit the trickle charger quick connect eyelets. (his instructions were pretty complex, even down to the order you have to disconnect them in) so to rule out batteries I would only feel sure it could solve the problem if both were replaced.

I think the Dealer should front that cost, after all if he doesnt resolve this - you will be returning the car? And he would have to do it anyway.

Please note I am not an expert like Malcolm or Craig ... my belief new batteries will resolve your issues are purely "based real world experience" of a very similar set of circumstances and symptoms - and to me pretty weird results, namely how a bad battery can screw up a car (allegedly because of low voltage) EVEN once you have it running with 14.4V! Albeit off the alternator"
I still can't phathom that set of facts.

But its now day 5, the battery shows 12.8V across the terminals all conneected, starts first time and the starter sounds very powerful. Seems to fire up instantly, runs perfectly. And has a battery drain of between 0.00A and 0.030A. ( which they say is perfect)
So all is resolved, and remains all good 5 days later.

 

[Submariner1]

Sent the dealer the bill for the batteries

Sounds reasonable as he only only got 5 miles!

 

[growla666]

Actually I quoted wrong - cost of replacing both batteries with (direct from Mercedes OEM) is £334 from the dealer. £147 starter/£131 AGM (ex VAT). My indy doesn't think it is a battery problem but am keen to remove this problem by buying 2 new batteries anyway. Submariners experience gives me some warmth at least.

 

[growla666]

Update - not battery

Just had indy come back and say its a CANBUS issue as they've found that the gear lever isn't talking to anything else and is intermittent. They've ruled out battery problem. They suggest it could be wiring fault or a bus problem and it will have to go to a Merc dealer because if they buy and attach any modules and it's not a module problem then they wont be able to get a refund on the part -so they recommend taking it to Mercedes. :cry::sad: