Battery issue.... W126, new alt
 

Well I have my new alt. Reading 14.1 to 14.4 at batt. So I am certain its good. I replaced the alt due to charging issues. I am certain it was heading south. But now I am wondering if its the batt.

Is the battery serviceable? Its a newer looking MB batt. Had quarter sized plastic screw caps on top. Battery does not say unserviceable like most sealed types.

Thoughts? Hate to get a whole new batt. Oh, in the morning I am reading just under 13v at batt. Nothing is left on overnight. Crankovers getting worse.

Your car won't crank easily with 13v at the battery?

At 13 it will crank "ok". But sometimes I read just over 12 and then its real bad at cranking. Its a very random/odd issue. Next step is to clean all grounds at battery. I installed a heavy duty ground strap from alt to body when I put it in.

Sounds like your battery doesn't like load very much. You can try to top off the battery with some distilled water. If that doesn't fix it, new battery.

battery
 

Autozone will test battery and alternator on the car for free. Worth a ride over to the nearest zone for the test

Never had any experience with a serviceable battery, which this one is. Checked the levels and one cell was lower than most. Not sure where to fill to. Most are up to the bottom of the plug which is about an inch deep.

Think I will get it tested as suggested.

Here in Texas we prize the water-addable batteries - they last 7-8 years vs the non-serviceable kind, which dry up in 2-3 years.
There is usually a formed-in split ring about an inch down in the cell which is the water level indicator. But, if the plates are well covered, then water level is probably not your problem.
The most common falilure mode for a battery with sufficient water/electrolyte is to still indicate 12.5 volts or more at rest, but it cannot take a load, and will drop to 5V or so when trying to start; and even the power windows will run slower. You can put a voltmeter on it, hit the starter, and you will know - if it drops below about 10 volts when cranking, it's a goner. We've had two with these exact symptoms this week.

DG

I will try the cranking voltage. But I did add water and it's seems to have helped. Did so after one of my posts above. Took about 1/5 gallon to top off.

Update on this. While the water did help the battery did die. One morning it would barley crank a half revolution. When I took it out, I saw the min/max lines. The water line, before I added, was well above the max. So adding more may not have helped much.

Either way for $84 I have a brand new battery with a 900 cold crank amp rating, twice as much as the Mercedes OEM battery I had. The car has NEVER cranked this well and after a week continues to work great.