The owner's manual for the 99E300 states that there is no maintenance required on the battery. There is also a warning that any relplacement battery must be able to be held upside down for a minimum of fifteen minutes without leaking so, to be sure that you get the correct battery, call Mercedes-Benz.
I looked at the battery located under the rear seat and noticed that it looked exactly like the battery in my 87300tdt, screw caps and all. The 99 has an additional feature--a clear plastic drain hose near the neagative terminal that leads under the car.
I also noticed that my electrolyte level was about 60% full.
A call to the dealer ensued. The reply to my question about refilling the battery was that if I was worried about my battery, just buy a new one. HUH! I could get no answer as to whether filling the battery was ok or not, or whether I had a truly Maintenance free battery or not, or whether the drain tube would leak. A call to MBUSA had the same result. No one had an answer.
but everyone suggested that I buy a new battery.
Does anybody know 1. What is a manintenance free battery? and
2. what is the right battery for the 99E300? and 3. Will it hurt to top up my battery?.
Also have any 99E300 owners looked under the seat to see what is in there?

I'm going right now. Stand by...

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

But seriously, after getting ofer the sudden feeling of being rich, I found the exact same thing you did. Giant white battery, about 1/2 full. Planning to get some distilled water and fill it up - I don't see any way that it could hurt.

Steve, the only battery I know of that can stand being upside down for 15 minutes is an Optima. I have one in my Jeep Commanche and it is fantastic. I plan to transfer it to the E300 when this battery dies. Actually, I'm surprised that the MB battery has lasted this long. The heat in Florida usually kills them after a couple years. Maybe the location has helped to preserve it.

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

I never noticed the maintenance free disclaimer in the manual of my 98 E300. It definately has the same battery - big white Mercedes Benz group 49, philips head screw caps and all. Maybe that same battery wasn't maintenance free in 1998

Anyways, I added distilled water to it for years. No problem. It just died last week, so it lasted 5.5 years - not bad. I replaced it with an Optima orange top - fits great, spins that diesel like it's a toy engine.

Jcyuhn,
Thanks for your reply. I see you are in the Dallas area. Whwere did you get your Optima battery?
Steve

"Maintenance Free" batteries were introduced quite a few years ago and aren't in fact really maintenance free. To the best of my knowledge only the gel batteries (Optima as an example) are truly maintenance free. The batteries you have should more accurately be called low maintenance. I think the advance in design was really nothing more than a venting system that limits evaporation of electrolyte. Notice the key word "limit" and not "eliminate". You do need to check the level on these (that's why they make them so you can add fluid) just not as often as the older style. These are standard technology lead/acid batteries so adding distilled water should be safe. Don't overfill it and check it at least once a year. Also, if you have truly been running them with half the fluid gone then expect that they will likely fail fairly soon due to sulfation (usually results in a cell going bad and a voltage drop). Not much you can do about that at this point.

This all makes the old trick about the waterproof vs. water resistant watch come to mind.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

I bought my Optima at Batteries Plus. They have a store locator here: http://www.batteriesplus.com

Or you could do a web search for Optima Batteries.

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

Thenks to all for the excellent replies. I shall go battery shopping next week.
regards,
Steve

Maintenance free is a marketing gimick. As pointed out the only maintenance free are the gel cells. Distilled water is the fluid for top ups. I worked at an automotive battery shop a number of years back , we would even top up batteries without removable caps(AC Delco) by drilling the case and resealing it. Another battery scam is for dealers to replace a battery when it is drained. They will tell you they charged it and it did not respond, don't buy this story unless it has been charged for min 12-24 hours at a relativley low charging rate. From working in this field I would estimate that half of all automotive batteries replaced are in fact still servicable. Average battery life is 5years. merry hoho

The water does not evaporate from batteries. Hydrolysis of the water occurs in the battery. This is the chemical decomposition of the water into hydrogen and oxygen caused by electrical current flow in the water.

Calcium was added to the lead in the plates as a catalyst which causes the gaseous hydrogen and oxygen to recombine into water instead of escaping into the air. Of course a small amount of oxygen and hydrogen still escape and that is why the batteries are not completely maintenance free.

P E H

I bought my Optima at Batteries Plus. There's a store on Central Expressway in Plano that I use. I believe there's also a dealer locator on the Optima battery website -

http://www.optimabatteries.com/

- Jim

Optima Orange Top is similar with Red Top with
reverse top post. The lowest price I found is
$105.90 at http://www.batteryweb.com/optima.cfm