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.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

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

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

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.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

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.

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

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

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'05 Ford Escape 100,000 miles
'87 560SL 92000 miles
'89 300TE 199,000 miles
'02 Audi TT 100,000 miles
'00 Ford Excursion V-10 121000 miles
'92 Mercury Capri 100000 miles
'02 BMW 325XI 60000 miles
'92 230CE 160000
'87 BMW 535SI 160,000 miles
'93 Rinker Captiva 209
5 Kids
2 Dogs
1 Wife

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.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

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.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

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.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car