Jud Chapin

In swapping out my aux. battery located in the trunk of my '16 S550 coupe, there is a venting tube for it. This is an AGM battery, p/n 000-982-96-08, so why did MB vent it? It's a PITA to hook up due to limited space so I didn't do it. Now I'm having seconds thoughts.

as.thompson

The documentation that I have read indicates these batteries are vented with a valve that only opens to relieve over-pressure, should any occur, internally to the battery. The vent is only opened if there is an abnormal condition.

Jud Chapin

Thanks. Funny, I've owned a few Vettes, 70's & early '80's, and the battery was in the back storage area inside the car. No venting on those.

Jud Chapin

Well, it's been eating at me that I didn't rehook up the vent so I decided to have another go at it as I'd rather be safe than sorry. Amazing what a snap this job is of swapping out the aux. battery once you've done it. Anyway, I got access to the battery again and placed the plastic angled vent part with the tube connected into the battery. Then with the battery in place, I sprayed WD-40 on the tube and it slipped right in to the car's vent hole in the trunk. Without lubricant, it's tough getting the vent tube where you want it due to limited space. The whole job took about 45 minutes as opposed to a couple of hours the first go around. There's a lot of confusing info out there on doing this job including MB's WIS. If my aux. battery were to need replacment again, I'm sure I could do the job in 1/2 hour or so. Keep in mind this is for the S550 coupe but I imagine the S550 sedan is basically the same.
Of interest is what this battery is called. I see where just MB has several names for it including auxiliary, starter, and additional (WIS).