[gtwibell]

Now my 451ED's 12v battery has started self discharging again (which we all know to be potentially fatal with these cars) I've begun investigating possible reasons. The first thing I've noticed is the gear position indicator down by the shifter remains illuminated permanently, even when the car is off and locked and the key is removed.

Does this happen on anyone else's ED?

 

[sokoloff]

Not on mine. That may indicate that the HV battery contactor is closed, the HV battery is in play and trying to charge your 12v battery. Do you notice the HV charge going down overnight more than it should? You are right that it needs to be addressed ASAP. When you say the 12v battery is discharging "again," how old is the battery, when did this happen before and could this mean you've got another issue to figure out?

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 18,500 miles

 

[gtwibell]

Len,
The 12v self discharging is intermittent. The first time was maybe four and a half years ago, just after we got the car s/h from an MB/SmartED main dealer. 12v battery was recharged and no problem thereafter. The second time was winter 2018/19. Car had been last used three or four days before. 12v again flat, HV System Failure on the display.
At this time my wife was in the hospital and I was more than a little distracted from car problems, but I did recharge the 12v again and used the ED every day, twice a day (indeed it was ideal vehicle vehicle for carving through city traffic) to visit her.
All well for a few weeks then a recurrence after a couple of days of non-use. From then on I was trickle charging every night and carried around a jump start pack and the car went back into regular use and I ceased trickle charging with no further problems.
I reported the 12v discharge issue to the dealer when I took the car in for annual service in October 2018, with about 50% SOC remaining. They read the stored fault codes, investigated further, and three days later pronounced both the 12v and HV batteries 'broken' and an unspecified module 'failed'. Over the next two or three weeks I watched (via the now RIP web portal) as the HV SOC gradually declined to zero. At this time I was unaware of the consequences of letting the 12v and the HV go completely flat. I guess the dealer was too.
I had the BAP and all the work and replacements were paid for by MB. I got the car back 8 months later (long wait for a new HV battery) and it has performed faultlessly for 11 months until two weeks ago, when I found the 12v dead once again. I've left it on trickle charge ever since, and the HV permanently connected to a charge point.
I'll be getting it back to the dealer ASAP but this time I have no BAP to rely on. Wondering if the dealer will offer some kind of warranty on the work done 11 months ago?
EDIT - I have the car booked for a diagnostic on 2nd July.

 

[sokoloff]

Usually a part replaced by Mercedes has a twelve month unlimited mileage warranty. Not sure if a warranty replacement in the first place is part of that. I think that the warranty may revert back to what the original part had. Something is definitely going on that needs to be addressed for sure. There was a service campaign that came out in about 2016 that some of us think might have addressed the 12v issue, but if you've had your car in since then, the dealer likely automatically would have updated it. There was no charge to do it and of course your new battery would have or should have already been updated. Not sure how much of a PIA the trickle charge is for you, but that is probably an easier thing to do rather than shell out $10K for a new battery. I'd definitely take the case up with the zone manager if the local dealership doesn't help.

Please keep us updated and good luck.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 18,500 miles

 

[gtwibell]

Good advice, thank you. I’m planning on fitting a permanent 12v charging connector wired direct to the battery and easily accessible from outside the car. Will give an update once the car has been in.