Guys, I cannot believe what is going on within the battery compartment of my clk55. i have only had it 3 months, it is an 03 model. I looked down inside the battery area and saw a puddle of water. Removed the battery, and the whole metal tray that it sits on is completely rusted up and swimming in water,as is the entire area underneath the same tray. The drainage tubes from the windscreen base are clear and do not leak into this area, I cannnot see where the water is coming from, Have any of you have had this problem ( maybe you should all take a look under your own batteries ), and what was the cause?. I cannot understand why there are no drainage holes in the floor of the battery area, it is an obvious place for water to collect and cause some serious rust damage.

 

Are you certain its just water?? Could be battery acid from a cracked battery case. Or, if it is water could be from someone who tried to service the battery and spilled it.

 

It is definitely water, and for the battery tray to be so rusted up so badly as to be perforated it would indicate that this has been ongoing on this car for quite some time. Have there been any TSB's for this problem as not having drainage holes in this area is just plain absurd.

 

Of course there's no TSB because it's not a common problem.

On YOUR car something is plugged, preventing designed-in draining.

In addition, the corrosion is most likely caused by battery acid as opposed to water. Batteries must be kept clean and battery trays often require at least painting if not just replacement.

 

lkchris, how do you know its not a common problem - I would not have looked in there had I not needed to take the battery out. I would'nt think that is something very many people would ever do themselves. If you yourself had a clk55 and had you looked under the battery tray you would know that there is no 'designed-in draining' underneath. Believe me I have looked. I also poured a little water into the same compartment on the other side of the car to see if that would drain and it just sat there for hours until it evaporated.

 

I'm aghast that they still use metal for battery trays. Smart automotive designers use plastic for the trays.

For preventive measures on ANY car that uses metal trays, I take the trays out, grit blast them if needed, and paint them with rubber paint... the same paint that is used for dip-treating tool handles. Treat all fasteners in the area with a good coating of antiseize compound. I've seen neglected trays rust to nothing from the battery acid.

Since your car is so young, do what the others suggested above. This is not normal for your car. Once you clean the area, treat the corrosion with a spray rustproofing compound to protect the metal from further corrosion.

 

Kestas, thanks for your reply. I have to ask, if the battery casing is not split, and there is no leakage from the caps at the top, then where is the acid coming from to do this much damage.Maybe this is a newish battery and the old one had a leak? I got my teenage son to wire-brush the rust off the tray, and then gave it two coats of Hammerite Paint(if you are not familiar with this product it chemically bonds with rust and stops further formation) Do you think this will be OK?

 

Are you sure this isn't the original battery? If it's a replacement, this may be a clue to the problem since the car is rather new. Acid damage may have come from the old battery. Regardless of whether it came from the old or new battery, it came from the battery.

I believe a car that is experiencing an overcharging condition can generate excessive hydrogen, which can bubble out some of the acid electrolyte.

I'm curious if corrosion is limited to the battery tray, or if there is also corrosion under the tray. I think you're doing the best you can to deal with the corrosion. I prefer sandblasting corrosion from metal since I have access to sandblasting equipment. After paint, I would cover the area with rustproofing.

 

Car batteries are not sealed. They have a vent to allow hydrogen gas to escape whilst charging. Sometimes people over fill the battery, and the sulfuric acid then sloshes out the vent.

If you have a new battery, is it from Mercedes? Their batteries are high capacity units, and battries that size are not generally available in the forecourt of a petrol station, or normal auto spares shops.

 

Some car batteries are sealed....spiral wound or flat plate gel filled batteries are sealed with only a safety valve (not a vent) to protect against excessive pressure. MB batteries have a vent with a plastic tube to direct the gasses/fluid to the atmosphere and away from sensitive points under the hood. If the vent tube is kinked/blocked/routed wrong it can cause problems. This is the longest (5 years) I've ever had a car battery and I attribute it to the size (100ah!) of my battery.

 

Did the rust appear quickly or over a long period of time? How often do you check under the battery.
Used to live near a river ford and my old car collected water everywhere. Ended up drilling holes (and rust proofing them) in quite a few places.

 

Did the rust appear quickly or over a long period of time? How often do you check under the battery.
Used to live near a river ford and my old car collected water everywhere. Ended up drilling holes (and rust proofing them) in quite a few places.

 

Hi Big Damage, I have only had the car 3 months and if I had not dropped a screw down into the battery compartment and then removed the battery(what a weight) to recover it I would never had seen the rust/corrosion down there. I also have drilled a hole down next to where the windscreen drain tube dissapears into the top of the wheel-arch as I found that rain goes down through the bonnet vent onto the air-con filter housing above the battery. The air-con filter housing has 2 short drain tubes for water drainage which (wait for it) goes straight down into the battery compartment, and then just sits there. A really clever bit of design !!

 

My model is different than yours but I have the same cabin pre-filter/cover arrangement. The tubes do not drain into the battery tray. Pop the hood/bonnet and pour water into the tray and see what happens. Mine flows outside the battery tray down to the road. Besides, I tend to agree that it's battery acid. Check the service record to see if the battery was ever replaced. Your car is too new for water to be the culprit.

 

Mleskovar, i assure you that the air filter which sits directly above the battery is designed to slope down towards two 1" long spouts at its base which drain water directly into the top of the wheelarch which houses the battery. have a look under the bonnet of a clk(03 onwards) you will see what I mean. I think though you may be right about the acid as the plastic tray under the metal tray which holds some pretty hefty cables looks to have been eaten away as well.once the acid had corroded the metal battery tray the water getting in just made the rust worse.

 

Mleskovar, i assure you that the air filter which sits directly above the battery is designed to slope down towards two 1" long spouts at its base which drain water directly into the top of the wheelarch which houses the battery. have a look under the bonnet of a clk(03 onwards) you will see what I mean. I think though you may be right about the acid as the plastic tray under the metal tray which holds some pretty hefty cables looks to have been eaten away as well.once the acid had corroded the metal battery tray the water getting in just made the rust worse.

 

Mleskovar, i assure you that the air filter which sits directly above the battery is designed to slope down towards two 1" long spouts at its base which drain water directly into the top of the wheelarch which houses the battery.On the opposite side of the car there is a plastic cover above the fuse area which again drains water into the top of the wheel arch with no drain holes. have a look under the bonnet of a clk(03 onwards) you will see what I mean. I think though you may be right about the acid as the plastic strapping under the metal tray which holds some pretty hefty cables looks to have been eaten away in places as well.once the acid had corroded the metal battery tray the water getting in just made the rust worse.