Heisenberg

Had the main (engine compartment) battery die recently, it was replaced by roadside. It failed spectacularly overnight, car wouldn't start and was giving me less than 10v when I hooked up a charger.

Now I'm getting a 'auxiliary battery malfunction' error sometimes, not always, when I start the car, a 2014 CLS63 S. I've checked the trunk battery (for ECO, I think) and it reads 12.9-13v with the car off and disconnected, so isn't dead and is getting charged.

So does the CLS63 have a third 'auxiliary' battery - maybe the small transmission backup battery like some of the E-Class models have ? I know it is hidden below the dash on those, but thought it was only used in cars with the steering column shifter stalk. The CLS63 obviously has a console shifter, although it is really just an toggle lever so functionally is probably similar to the stalk shifter.

I'm sure the dealer would fix it under warranty if I bought it in, but if it just needs a cheap 12v lead acid battery with standard connectors, I'd just buy one and install myself. But I don't want to take a bunch of panels off, if it isn't in there...

evansw220

Eco Start/stop battery is called the Auxiliary Battery.. They tend to fail due to high internal resistance...

delirium

I got an auxiliary battery malfunction too. So, do I replace the battery in the trunk or do we have a battery in the dash as well?

kponti

As far as I am aware we only have two batteries, main one under the AC air inlet under the hood and second accessory one in the truck.
I just changed both of mine recently and those were the only two batteries MB gave me options for