SO, I have had my car now for 4.5yrs so I think that I know it quite well and I think it is now fair to say that the stop start has stopped working about 2 months ago. Yes there have been some cold days, but even after a 400km drive and my Mercedes Me App showing the starter battery as "fully charged" there has been either no start stop or literally a random stop start and then nothing for weeks now. Three weeks ago I got 3 in a row and then nothing (was only stopped at the lights about 10 secs each time).

I bought a battery health tester today and the figures for the 80Ah 800A original battery were: CCA 650, SoH 66, SoC 61 and v 12.37. Outside temp is currently about +5c and the car has been driven about 75km today. The battery is the original (week 37/18) and the car has done about 125k km.

Do these figures point to a battery problem, or a charging problem? There are no fault codes being picked up by my fault code reader?

Help!

 

You are more technical than I am, but I've also had my car for about five years (on the original battery), and the stop start engages noticeably less frequently over time. I *think* it is more influenced by colder weather and periods of lower use. There also seems to be a certain randomness to it. It might shut off once, and then it doesn't shut off just a few minutes later. It wouldn't surprise me if there is logic to be more conservative as the battery gets older, even if it's still working well. I'm not inclined to replace the battery, unless I notice it sounding sluggish on startup, but that's just me.

I always thought the function was fairly useless. If I just barely stop as I'm pulling into a parking space, the car would shut off. If I was stopped at a traffic light for more than a minute, the car would start up again. I really don't think it's saving the planet.

 

Sooner or later you will get a Aux battery malfunction on the dash and then it's time to replace that little Aux battery. My car does the same thing even here in very warm Florida. After 4 or 5 years the Aux battery is pretty well spent. When you get the Aux Battery Malfunction then you adaptive Cruise will not work any longer either until you can get a new battery in there.

 

UPDATE: So my battery was trickle charged full last night and my MercedesMe App says the battery is fully charged. So far so good, but driven to work [35km - all moving A road or motorway] and putting the tester on the car now says:

V - 12.13v (was 12.37
CC - 660 (was 650)
SoH - 71% (was 66)
SoC - 13% (was 61)

Very confused - WTAF?

 

Does this W213 have any aux battery? I thought these have the capacitor instead. The one that fails quite often on a W205.

 

I am 99% sure there is no aux battery, only the voltage regulator in the footwell. Only one better shows on the rescue card if you scan the QR code.

 

I had the same problem and was at the dealer today. When stop/start stops working, it’s time for a new battery. Dealer installed a new battery and auto stop/start is working again. I can still turn it off when I don’t feel like using it but it is sort of a proxy for a failing battery. I’m glad I could change it before it actually died.

 

The question is where to get a good deal on a battery with install for a e450 wagon. I know the dealers stock them but I’m sure like everything else very expensive. I looked it up at autozone, Oreilly and batteries and bulbs and nobody seems to carry this battery. Anyone have any ideas?

Plus I understand it’s best to replace the voltage regulator (aux battery) along with the main battery. I don’t really look forward to replacing the voltage regulator as it’s in an awkward spot in the pass footwell and a lot of stuff needs to be removed. With this issue of auto start/stop not working I’d think it’s more than likely the aux battery (voltage regulator) and not the main.

I do notice though when I charge the main battery with my battery tender everything works fine for a while. I’d think charging the main battery also charges the Aux. must be a capacitor or two is bad in the aux? Kinda seems like under engineering to me I’m surprised I got 4.5 years out of it. Plus for a maintenance item like the aux you’d think it would be in a more accessible location.

 

Additional update: MercedesMe App days Car is now charged by SS today. Temp is +6c so should work. Battery test said CCA 761, SoH 85% and SoC 23% and voltage is only 12.13v

Spoke to some technical people at work today who know about these things, they are 99% sure that one of the cells is breaking down, hence the random readings and that the Alternator is doing most of the work. Clearly all is not well so I will bite the bullet and get a new battery (about €150 delivered here in Germany but not a “Mercedes” one)… I’ll let you know how I get on.

 

Are you certain you have an auxiliary battery? They switched to capacitors from a second battery sometime before the 2017 models, but I can't say 100% that they didn't bring them back for 2019.

You don't need to replace the capacitors with a battery change.

 

They call it either the voltage converter or aux battery but it sits near the glovebox up in the passenger side footwell. It’s a bugger to get to lots of stuff has to come out. You can get ‘em cheap on Amazon. Hella is a decent brand. I’ve seen them as low as 25 bucks. The main issue is the pita labor. My car won’t do stop start at all at this point. As long as adaptive cruise and brake hold still work I’m not doing it. When those quite I’ll get the voltage converter box replaced. The little capacitors wear out.

 

Final Update: I replaced the battery (not a Varta but another "German" brand) with the same Ah/CCA. After running the car for 5 mins to get it fully charged, SS has been working faultlessly - even this morning with the outside temperatue at 1 deg C! I did reset the Battery Life in the Front SAM becasue I have the technology to do so, however, I don't know if thi is strictly necessary?

Job Done