W205 C63 - Battery Draw issue?

[Loko]

Hi there folks,

New to the forum after buying a W205 C63 5 months ago. Car has been great and enjoying it very much. Has been faultless up to now. It's a 2015 car with 32k miles. Full MBSH with every correct item. It had a new Mercedes battery fitted in Nov 2020 by previous owner, I have receipt.

It's been in the body shop for new rear bumper & paint, I picked the car up on Thursday last week after being a week at body shop, stopped at 3 petrol stations to fill up on that day and eventually parked up at 5pm at home. Went to unlock car on Sunday 11am and it was completely dead, i.e. after around 66 hours later. I've been leaving the car at times for 2-3 weeks previously a number of times (COVID plus use of other car) and has always started fine.

I measure the battery and its at 4.8V. Greenflag comes out booster on, starts up. The chappy did a battery test with his little device and it says replace battery. Bizarrely, it was idling for 4mins tops. Turned it off, booster off, cranked it again on its own power and it started up no hesitation. He measured the voltage and it's at 14.7V, i.e. alternator seems to be fine. Turned off, and battery reporting 12 point something.

I went for an hours drive and so far so good. I know it could be the battery but I was thinking unlikely and whether the bodyshop has done something that could have upset it, but in principle should only have disconnected things like parking sensors.

I'm then drawn to the fact there must be a battery drain on the car. I've done an amp pull test very crudely but I can't read too much into that because various modules are awake and haven't had a chance to go through the effort of tricking the car into doors, etc. being closed to lock it, pulling fuses whilst measuring current on negative terminal, etc.

I then recalled the Workshop menu which you access on W205 by putting accessory mode on (first click of key or first press of keyless go button in my case) and pressing ok and pick up call buttons on steering wheel, has a page where it reports battery voltage, battery current, battery temp and charge %. I access said page, and with everything off and doors shut sat in the car it's reporting 11.2A draw on the battery. That's not what the real draw is when everything is locked and car is dormant, since modules will be awake, etc. but I'm assuming there is extra draw on that number if I have a drain. Could a W205 C63 owner advise what his/her current draw is in accessory mode on with doors closed and all off (radio, etc.) based on the cluster menu?

The battery seems to drop around 1% percent per hour, i.e. 1Ah drain if one trusts the battery % charge the car is reporting. I've topped it up with my CTEK MXS 5.0 and the car reports 12.7V and 95% charge when it's done charging and trickling. If I leave the charger on and I turn on accessory mode to monitor voltage and then wait for a 1-2 minutes, the voltage starts to drop from 12.7V to 12.2-12.3 volts and stays there whilst battery % charge drops. Goes from say 95% to 90% over say 5-10mins. Car showing -6.5A drain with charger on and -11.5A drain with charger off (i.e. seems to be reporting the 5A charge correctly).

I know first step is change battery, but wanted to do some investigative work which may help. It may be coincidental, but wondered if there's something the shop may have done. Is my best bet change the battery and take it from there? If someone can advise on their car's reported current drain in accessory mode and that is -11A too, I guess that would confirm car's ok.

Sorry for first long post!

Thanks!

 

[Loko]

I also forgot to ask, if I replace with a MB battery does it need coding or can I just bolt a new one straight on?

 

[Petrol Pete]

Welcome along Loko. Long first post a problem ? On the contrary , we sometime get first posters on here needing help but just say something like

" I have a MB ( a white one) and the battery goes flat..help...NOW !! "

And they then get stressed and abusive when we ask for a little more. Your post gives loads of info. I do think you are going to have to go through the 'tricking the car' thing so it goes to sleep completely to get a better chance at finding the fault.

You seem to be up to speed so forgive me if this youtube is something you have already seen . Good luck with it .

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

 

[Loko]

Thanks! All info is good info. I found a similar video that was very detailed and helpful, will post later for reference for folks.

I guess my initial questions were:

A. Do folks agree 11A draw as reported by the car when in accessory mode is high? I guess a 1 or 2A parasitic draw hide itself in that number? Battery is lasting 36hrs ok, but if car can be trusted it’s depleting the battery - reporting say 70% charge after that time.

B. Given the recovery guy said his battery test said replace, should that be the first try? I was thinking I could disconnect the battery and check that it holds charge that way. I would replace out of course but being only 11 months old didn’t want to throw £200 at it for a lower likelihood cause. I wondered if the battery tester would give the right answer if the battery was low on charge / had a current draw on it?

C. Wondered if another W205 C63 owner could report his battery drain per the car when in accessory mode I might spit a large discrepancy but technically that might be option specific and not give too much insight if the drain is only 1A say.

 

[Blobsta]

" I have a MB ( a white one) and the battery goes flat..help...NOW !! "

Hahaha. Yes, this. every time!

OP, great descriptive first post with lot of info, excellent job.

I'd always look at "what has changed" but it's hard to imagine in this case that paintwork on the rear bumper could cause this issue.

Personally I would go through similar steps to the video, open the doors/boot/bonnet and then shut the latches over so that the car will 'go to sleep' and measure your battery drain at that point. Anything close to 1a or over is too much for a vehicle at rest I would think. If your battery went down to 4.5v that is really low and it is odd that it recovered so quickly on a jump pack isn't it? I have suffered a battery issue like yours but in a very basic van years ago, it started fine in the morning and I drove it all day (doing multi drop parcel delivery), jumped back in it on a farm after a few minutes stop and it was utterly dead. we jumped it and then left it running fro the remainder of the work. Couldn't find any fault at all and then replaced it never to see the fault again.

To address your questions specifically, my thoughts would be:
A: probably not (IMO), there is a lot going on when you have the ignition on.
B: Based on my personal experience I probably would replace but do some basic testing first as mentioned above.
C: I don't own a C63

Keep us updated and please report back when you find the cure.

Richard

 

[Loko]

Hahaha. Yes, this. every time!

OP, great descriptive first post with lot of info, excellent job.

I'd always look at "what has changed" but it's hard to imagine in this case that paintwork on the rear bumper could cause this issue.

Personally I would go through similar steps to the video, open the doors/boot/bonnet and then shut the latches over so that the car will 'go to sleep' and measure your battery drain at that point. Anything close to 1a or over is too much for a vehicle at rest I would think. If your battery went down to 4.5v that is really low and it is odd that it recovered so quickly on a jump pack isn't it? I have suffered a battery issue like yours but in a very basic van years ago, it started fine in the morning and I drove it all day (doing multi drop parcel delivery), jumped back in it on a farm after a few minutes stop and it was utterly dead. we jumped it and then left it running fro the remainder of the work. Couldn't find any fault at all and then replaced it never to see the fault again.

To address your questions specifically, my thoughts would be:
A: probably not (IMO), there is a lot going on when you have the ignition on.
B: Based on my personal experience I probably would replace but do some basic testing first as mentioned above.
C: I don't own a C63

Keep us updated and please report back when you find the cure.

Richard

Thanks a lot for the help!

Overnight it was connected to ctek in AGM mode, went to car this morning to find it was still charging and at 88% according to car. It started charging at 10pm at 85%.

The previous 2 days overnight starting from 70 to 80% charge, the ctek had finished its cycle by the next morning and was trickling. Not sure if that suggests the battery is indeed suspect. As you say it’s weird it would recover from 4.8V to be able to start the car after 4 mins of idle (car suggests it pumps circa 45A into battery for 2-3mins in the testing I’ve done, then goes down to 13A ish and drops to 1-2A when battery at 95%).

Your exactly right, I try to look at what’s changed and think back. One other piece of info, the brake pad wear warning did pop up from the time I collected the car from body shop. The car has been driven less than a mile whilst they’ve had it. The front pads were at 1.8mm during last service at MB in July, so could just have trickled on by coincidence. Could the pad wear sensor being open circuit cause a drain? It shouldn’t right?

I think I’ll get a battery tester from Amazon and test battery connected and disconnected from car and/or disconnect battery, fully charge and see if it holds 12.6-12.7 volts overnight when disconnected from car.

 

[Loko]

Quick update, after 4 and a bit days battery voltage is 12.35V which is about 75% for an AGM. Started the test at 12.5V which is circa 90%.

Battery tester is reporting internal resistance as good and producing most of the 850CCA. It’s a bit erratic and non consistent though. I am measuring it connected to the car so the load on the battery will affect this.

In short, haven’t got around to doing the parasitic test as been snowed under with work. My main concern is that because it got down to 4.8V measured, whether it’s adversely affected the battery. I’ll continue to monitor and see if it lasts till the end of week and also disconnect from car to run tests.

If the car did have a drain it should have flattened the battery by now compared to the time it took first time it happened. The mystery continues…

 

[190]

B. Given the recovery guy said his battery test said replace, should that be the first try? I was thinking I could disconnect the battery and check that it holds charge that way. I would replace out of course but being only 11 months old didn’t want to throw £200 at it for a lower likelihood cause. I wondered if the battery tester would give the right answer if the battery was low on charge / had a current draw on it?

A very good question. I would not trust the diagnosis of the recovery guy given the battery was tested a few minutes after being resurrected from dead flat. I think it would be impossible to test a battery that is near dead especially when it has a current draw on it. For the most accurate result it should be fully charged first.

You did the right thing to charge it with a battery charger as driving for an hour is not going to come near to doing it, I would though have charged it for several days as a 100Ah battery will need in excess of 110 Ah put back in to fully charge it.

Ultimately to test the battery accurately it should be disconnected from the car, truly fully charged and then left overnight to dissipate the surface charge before measuring the voltage. An AGM should then read in excess of 12.8 volts. There is a possible bonus in doing it this way. I have had an excess current draw on my car in the past and it was cured simply by disconnecting the battery and leaving the car overnight. You have the hassle of resetting things but it might be worth a try.

 

[Loko]

Quick update, after 4 and a bit days battery voltage is 12.35V which is about 75% for an AGM. Started the test at 12.5V which is circa 90%.

Battery tester is reporting internal resistance as good and producing most of the 850CCA. It’s a bit erratic and non consistent though. I am measuring it connected to the car so the load on the battery will affect this.

In short, haven’t got around to doing the parasitic test as been snowed under with work. My main concern is that because it got down to 4.8V measured, whether it’s adversely affected the battery. I’ll continue to monitor and see if it lasts till the end of week and also disconnect from car to run tests.

If the car did have a drain it should have flattened the battery by now compared to the time it took first time it happened. The mystery continues…

A very good question. I would not trust the diagnosis of the recovery guy given the battery was tested a few minutes after being resurrected from dead flat. I think it would be impossible to test a battery that is near dead especially when it has a current draw on it. For the most accurate result it should be fully charged first.

You did the right thing to charge it with a battery charger as driving for an hour is not going to come near to doing it, I would though have charged it for several days as a 100Ah battery will need in excess of 110 Ah put back in to fully charge it.

Ultimately to test the battery accurately it should be disconnected from the car, truly fully charged and then left overnight to dissipate the surface charge before measuring the voltage. An AGM should then read in excess of 12.8 volts. There is a possible bonus in doing it this way. I have had an excess current draw on my car in the past and it was cured simply by disconnecting the battery and leaving the car overnight. You have the hassle of resetting things but it might be worth a try.

Very good, sounds like a plan. So far it seems to be holding itself ok ish. I’ll have a go at disconnecting & charging on the CTEK and leaving overnight to dissipate the surface charge and then testing. Providing my seat doesn’t move and I can save the position into memory again I’m not fussed. I hate it when you spend forever dialling in the perfect position and you lose it never to find one quite so good again.

 

[Markw70]

If you have the receipt and the battery is less than 1 year old and you suspect it might be faulty, would it not be still be under guarantee?

 

[Loko]

Very good, sounds like a plan. So far it seems to be holding itself ok ish. I’ll have a go at disconnecting & charging on the CTEK and leaving overnight to dissipate the surface charge and then testing. Providing my seat doesn’t move and I can save the position into memory again I’m not fussed. I hate it when you spend forever dialling in the perfect position and you lose it never to find one quite so good again.

If you have the receipt and the battery is less than 1 year old and you suspect it might be faulty, would it not be still be under guarantee?

I do yes but it’s in the previous owners name, I don’t know that it’s transferable?
I guess they’d charge me diagnostics fee to establish if the battery is deffective. I’ll have to ask.