bob58d

Thanks. Finding that video was a godsend. I never would have thought of it and I was not looking forward to the de-panel job.

The carpet in that location is very stiff and, after I replaced the battery, I used some Gorilla tape on the back of the cut seems to give it a little support. I don’t think having cut that carpet is going to limit me from putting anything there that I would normally consider putting there.

sub786sub

Question what is the use of the 2nd Battery? What it powers?

kptaylor

Thanks @bob58d! This made it much easier, basically a 5 minute job. The only issue I had was the size of the battery you used. I too have a 2014 ML350 4matic and the aux battery is much smaller than the one you linked to on Amazon. Mine is MB# n000000004039. Returned and reordered and everything is working just fine! The larger battery fit into the hole but I couldn't figure a way to use the hold down bracket so the battery would have flopped around in there.

threeMBs

The carpet cutting method as posted in post #24, I speculate will only work if the specific W166 ML is equipped with small "4039" aux battery. However, if vehicle is equipped with larger (by quit a bit considering it is a very small place to "work" in), p/n 0009829608 (old p/n 019822708) it may not help as there is no room that I can see to work in. I assume the more equipment car has (DAP, etc.) the more likely it is equipped with the larger Aux battery.

I cut the carpet in my ML63 (it does not need the aux battery but was curious) and it seems there's no room for hands and tools to take the larger aux battery out:

Brent S

You can remove/re-install the small aux battery without cutting the carpet, and without removing the entire passenger side trunk liner (panel).
I just did it.
Wasn’t easy, but it’s possible.
I didn’t want to remove side trunk liner, because I didn’t want to pull off the trunk’s rubber seal.