At cruise speed voltage is 13.96 VDC steady.
Engine off its 12.05
Heater in Residiual heat mode it drops to 11.7 VDC at once and in less than 5 min it is down to 11.50VDC. At that time the battery insignia shows up in the heater control window and it shuts off..
I am looking hard at the battery.. I put 100 Amp load on it for about 15 seconds and it held on at about 11.21 VDC..
Is it the battery or could it be the alternator is not bringing it to full charge with only 13.96 VDC max charge voltage ?
Thanks for the help..

 

14 V is normal charging voltage. Sounds like the battery. How old is it?

 

I got the car used and it is a aftermarket battery that has no date punched on the label. I am gonna guess 3 yrs.

 

I have an '03 E320 which came with OEM AGM technology batteries. These AGM batteries require a slightly higher charging voltage. Is your battery a wet acid type? If so, than the charging circuit is overcharging the battery and will eventually kill it assumin gthat your model requires an AGM battery. A fully charged AGM battery should read about 12.8 volts where a wet acid battery would read about 12.65 volts.

Regards,
paul...

 

To me looks like a bad or marginal battery. Could also be the wrong spec battery since its not OEM. Replace the battery with the correct spec battery and it should be OK.

 

A S600 has alot of electronics running in the background so a high capacity battery in crucial.

Go get yourself a MB AGM battery of the largest size about 860-950A or equivilent (dry cell) and you won't have to think about it for at least 5 years.

 

OK.. will go looking for a battery.. Sounds like the AGM glass mat is the battery of choice these days.. I have a Interstate in it now..
Thanks for the response..