Your battery is fine. Unless you've previously let it go dead a few times (which damages it), you have several years of life left. Batteries last exceptionally long in the W210 due to its location. Getting 10 years out of a w210 battery is not rare or unusual at all. Under the rear seat, it's insulated from the engine heat cycling and vibration that shorten the life of batteries installed under the hood. W210 batteries have a cool, comfortable, smooth ride there under the back seat. Nothing unusual about the battery, it's a standard Group 49 or H8 size.

I just replaced the battery in my '98 E300 this year 2017. The old one I took out had a date of April 2006 on it.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

Funnily, that has not been my experience with our 98 E320 which has not been driven much in winter. It has had more batteries in the 17 years we have had it than any of our old cars. Even my winter driven 85 300D that has 430k km on it. It will at least "try" to start

Reason for the E320 battery problem is that if the starter pulls the system voltage much below 10V, the computer prevents the car from even trying to start. Car become completely dead. You can check the voltage during normal starting using the Climate Control display.

Sometimes recharging the battery will allow the battery life to be extended for a while. But before long, it will happen again. Turn key and nothing happens - and this not even in winter!

CCA (SAE method) is not the greatest measure given the above low voltage problem. 7.2 volts - not good enough on the gas W210!

CCA using DIN method seems more useful for computer controlled cars.

Hand held CCA testers are apparently not too accurate. More here
BU-902a: How to Measure CCA – Battery University

Don't know if this is true on the W210 diesels. Maybe the electronics are different?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5