Battery Under the Back Seat - Bad Idea
 

I noticed that my starter wasn't turning over as quickly as it should in really cold weather and immediately suspected the battery. I've only had this car ('97 E300D) a couple of months and hadn't looked at the battery yet. I was a little nervous at first knowing that the battery was under the rear seat - everything is probably rusted out - but decided that since the car is so new (at least by my standards) that everything would be fine.

I removed the back seat and sure enough, the floor was covered in that white sulfer powder and was full of light surface rust. Not to mention it had a NAPA battery. I cleaned everything out as best I could, added water to the battery and put grease on the posts. It starts a little better now. I still need to go back in there and spray down some Extend to take care of the light rust before it gets bad.

I almost forgot to mention that the battery had some type of connection at the top for a drain?? or something. It connected to a rubber hose on the car which drained out through the floor pan. Of course, it wasn't hooked up.

I don't know why they put the battery under the back seat of these cars. I generally don't think it's a good idea because people forget about them and then its starts to rust like it did on mine. One thing is for sure, it will not rust any more as long as I own this car.

Scott

That tube is a vent so you don't get a buildup of hydrogen gas under the seat, causing an explosion. If you buy a new battery make sure it has the connection for a vent tube.

That's comforting to know...:)

I'd get rid of the NAPA battery (probably the original battery failed just before the lease was up on the car, and the owner was too cheap to buy the correct battery).
Clean up everything and install an MB battery with the hole for the tube.
In answer to your question "why is it there", just look around and tell me where else it'll fit? It's all space management these days. Plus the battery is a fairly heavy component, you get better weight distribution with it there. It's a safe enough location for it if it's vented outside as intended.

Gilly

trunk
 

The battery for my CLK55 is in the trunk.... better for traction (which is a little lacking on this vehicle since it is essentially a c-class chassis)

I guess I'd feel a little better with it in the trunk, like your CLK, or on the C class (202) chassis or S class or SL(129). But the main point is there is rarely room under the hood in the present styles, although they seem to be changing things around so much that now it's hard to predict where the battery (or batterIES!) will be on the newer models. On the new C class, they did manage to find a crammed-in spot under the hood, although you need to take a part off to get to it, you can barely see it, let alone service it. Now the new E class has one dinky battery (like a cycle battery) buried in the under hood area, the real "grunting" battery is in the trunk. The new SL has 2 decent-sized batteries, again one in the trunk (the bigger of the two) and a smaller one under the hood.

Gilly

What do you mean you put grease on the posts?
Get those little red and green felt washers to put under the wires... but never put grease on the posts...grease is not a good conductor of electricity...

I always put grease on the posts to keep the cables from corroding. I know that grease is not a good conductor but I don't think it affects the conductivity any in this application. I've never had any problems in the past. Is this not a good idea?

Scott

I think that he meant that he put grease on the posts AFTER the terminals were in place and tight. This is a good thing to do to keep corrosion under control. The WRONG way to use grease is BETWEEN the terminal and post.

When I was in the Army it was required that grease be spread over the battery terminal after it was tight and in place. (I'll bet everyone thought that the Army only had horses and mules back in the days I was a GI.)

I think that under the back seat is an EXCELLENT battery location. It frees up room under the hood and goes a long ways toward better weight distribution.

Have a great day,

Not to mention less exposure to extreme temperatures.

Audi put them under the back seat thru the 80's. Not sure if they still do.
Bummer part about putting them there is if you need to do a jump start. Less than convienient.

I should rephrase my initial statements regarding batteries in the back seat. There are probably many good reasons for having them back there AND if the car owner takes the time to service the battery and make sure it isn't rusting a whole in his floor plan, it's probably a great idea. I just think that hidden away under a seat, it's more subject to neglect by people who don't take care of their cars. But then again, these kinds of people probably wouldn't care if it was rusting everything away under the hood so it probably doesn't matter. :(

I have a replacement InterState bettery in my E. I didn't see any holes for a vent tube though... Any thoughts guys?

Sorry, but I have a problem with using an Optima battery in a W210. It does not have the vent tube connection. Now Optima says their battery will not gas in most conditions, but they did not say it won't gas at all. So under extreme charging conditions, there is still the possibility of a hydrogen buildup. Not something you want under your rear seat.

michakaveli - have you looked under the seat at the myriad of electronics under there? I think a spark might be possible. Combine that with a hydrogen cloud trapped under the seat, and the results could be nasty. That's why Mercedes put the vent tube in. I would get that battery out of there.

You guys might think I'm being alarmist, but why take a chance?

i had the battery in the wif's jetta blow up this past summer..
not a good thing to say the least:eek:

the damage was contained somewhat as there was a battery cover in place surrounding the top and sides. it still took a long time to clean up with plenty of water/baking soda.

i cannot image the mess if it had been mounted underneath a seat and likely with no cover - acid everywhere!!