Does anyone have a picture/video showing how to remove the OEM battery from a ML400.
I see them for ML350's and it seems my battery is installed differently (90 degrees?) from the ML400

 

They are all installed the same.

 

I did this today, its not the most fun. Have to trim the carpet and remove the vent/cover under the passenger seat. Very ungainly, tight fit. Have autozone do it.

 

What brand battery did you install? I can't find the Bosch battery in town, but Costco has the AGM Interstate (identical form factor to the MB battery) readily available. I have had great success with Interstate batteries in my other cars, but have never bought their AGM before.

(any value to putting a small 12 v battery across the charging bolts under the hood to keep the computer energized when replacing the main starter battery? (or will the auxiliary battery do that job))

 

The battery brand was Interstate, it was size H8. The car seemed to like it just fine. Normal operating procedure calls for a power source to be hooked through the OBD port while changing batteries. This serves two purposes, to maintain voltage for all the onboard computers while removing the power source, also, to insulate those modules from potentially damaging shock that occurs when connecting or disconnecting a charged source.

I would purchase a device to maintain power during a battery change if you plan on doing this yourself. Some devices will plug in through the OBD port, while other outdated devices used the lighter/charger. That's what I would do.

 

Buy the battery from the MB dealer, their prices on batteries are not far from retail at a parts store, plus you are sure to get the correct part.

 

There is an absolute zero chance I'd allow a lacky from autozone change a battery in my '87 jeep to say nothing of my (somewhat more complicated) mercedes.

 

I agree with Chassis. Got my MB branded AGM for maybe $10 more than the correct Bosch online. I dont think the interstate has the little vent nipple either. Since sits inside cabin, offgassing is vented thru a little tube. Replace the Aux battery at same time (same deal as main, maybe $5 more at dealer).

 

Does the auxiliary battery keep the computer and related systems powered while the main starting battery is removed?
I don't want the emissions system to reset (inspection will fail until the car is driven through its cycles).
I can put a 12.5 volt across the battery posts in the engine bay, but if the auxiliary battery is doing the same thing, no need.

 

Not really sure. When I replaced mine, nothing reset during the procedure, so it either has a capacitor or the Aux keeps it powered for the hour or so the main is disconnected.

 

I just found out that the auxiliary battery does indeed keep the computer memory from resetting. So no need to put a 12v source on the terminals under the engine bonnet.

 

Just make sure to keep the (+) terminal away from any metal bits (grounds) and it'll be fine.

 

Correct, WIS does not call for this. Click the DIY in my signature.

 

All done .... It was a pain in the @#)@%$, but straight forward.
The only issue is the weight and awkwardness of it all. The videos made a big difference - which gave me no surprises.

I installed an Interstate AGM group 49/H8 900CA replacement. It is identical in form factor to the OEM Mercedes.
It has the vent tube and it fit perfectly as expected. During battery removal, I had the new battery on a tender which brought it up to full charge.
After installation and starting the car - WOW - I am so glad I did this. The car cranked with zero effort compared to my 7 year old OEM which was clearly on its last legs.

Some tips if you use Interstate:
1. Keep the Mercedes red positive terminal battery cover which came with the OEM. It is slightly 'deeper' than the Interstate cover plate and will better cover the terminal wire bolt.
2. Be sure to use the vent plug which you have to bend off and remove from the Interstate positive terminal cover and plug the vent hole on the opposite side (next to the "+" terminal).
The vent tube will plug into the vent hole by the negative terminal as before.

Total cost = $184