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!
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!