2015 W212 auxiliary battery problem, again.

[C7pg]

I replaced the aux battery 3 years ago and today I had the aux battery malfunction message again today. How long are these things supposed to last? I can't check it right now as we're on our way back from Spain without the icarsoft. The one factor in both failures, if it is another failure, is that they both happened while away in Spain where it's been very hot. Surely that wouldnt affect it?

 

[Diesel Benz]

Similar battery as on my V222 but a different part number. I just changed mine second time at 7+ years and 50 000 km. The original part seemed to have a high failure percentage. At the time I changed it first time, a new part was available. I don't know what happened, I tripple-checked the first new battery was the new part but now when I changed it the second time, I found out that the second one had the same part number as the original one from factory. The car has not suffered from Spanish heat unfortunately.

 

[C7pg]

I've now tested the auxiliary battery voltage and its holding at 24.8 or so. Much the same as the main battery. Its charging at over 14 with the engine running so I reckon the alternator is fine. Icarsoft doesn't throw anything up either so I'm mystified why its showing a malfunction? Any ideas? I'm tempted to get a non mercedes battery, there are exide ones for around £45 around. Better that the arm and a leg Merc price. Anyone got experience of these? Thanks

 

[DrNick]

Bought a relatively cheap motorbike battery a few years ago - same part number. Its still going strong. I think it was around £30. Mine is a W212 estate petrol and the battery was in the boot if I recall. If you have a saloon it may be elsewhere and possibly a different physical size, so just check that. (I think yours is an estate, but I'm keeping it general!)

 

[Diesel Benz]

I've now tested the auxiliary battery voltage and its holding at 24.8 or so. Much the same as the main battery. Its charging at over 14 with the engine running so I reckon the alternator is fine. Icarsoft doesn't throw anything up either so I'm mystified why its showing a malfunction? Any ideas? I'm tempted to get a non mercedes battery, there are exide ones for around £45 around. Better that the arm and a leg Merc price. Anyone got experience of these? Thanks

A typo there, should read 14.8 V? The start/stop battery that I replaced most recently had a very good steady state voltage but if I tried to load it with 21 W bulb, the voltage dropped dramatically (something like less than 10 V). 21 W load is nothing compared to what the battery should normally feed.

 

[C7pg]

A typo there, should read 14.8 V? The start/stop battery that I replaced most recently had a very good steady state voltage but if I tried to load it with 21 W bulb, the voltage dropped dramatically (something like less than 10 V). 21 W load is nothing compared to what the battery should normally feed.

Yes of course should have said 14.8v. the 12.4 was with the engine off.
Yes the battery is under the floor at the back next to the Adblu tank.
I'll see how it goes the next few days, and then go for a non Merc one if I need to.
Thanks

 

[C7pg]

I decided to fit a new battery so got an Exide one at a quarter of the cost of the last genuine MB one. The missing functions appear to be back but when I tested the old battery it was at 12.7v. I was expecting the malfunction to lead to low voltage. Other than a small amount of white corrosion around the +ve terminal all seems ok with the old battery. Have I just wasted £40 odd?