Hello everyone, thank you for replies.
I got to Costco today, returned the beast of the battery and got a new one.
This new one has
735 cranking amps at 32 degrees celsius,
590 when cold,
The reference book that was there said that the original equipment cold crank amperage was 550. (1986 to 1992 300E)
I understand now that the higher the amperage, the more power to start.
Of course, I bought 12V batteries as the car is based on 12V.
Well I installed the battery, which fit depth and length wise, but damn did Mercedes use a very very wide battery originally. I wonder where you could find a battery that fits the tray in entirety? I am guessing the white box Mercedes-Benz battery?
Anyways, engine fired up within 1.5 seconds of crank.... I love this car!
I wonder what was wrong with the first battery, obviously, as I have learned, higher amperage is really only a good thing... I noticed that my first battery was manufactured on 9/2007 and the second one on 12/2007. Do car batteries have short self lives or did I just get a dud? I made sure that the posts did not contact to hood of the car, so that was not it.