There is a guy on cumminsforum that Ron's his house on batteries and swears that having a maintenance charge that balances the charge between cells greatly extends their life.

Not all chargers have that option. Apparently CTEK chargers do.

Could tell it's getting weak. Measured 575 CCA. Replaced....ready for New England winter.

__________________
06 E320 CDI "Benson", Platinum Blue on Grey, 187k mi, Stage 1 tune, tuned TCU
06 E320 CDI "Rutherford", Black on Tan, 160k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 139k mi, wastegate conversion

19 Honda CR-V EX 46k mi
Thirteen other MB's owned and sold
1961 Very Tolerant Wife

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?

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