Check out my post elsewhere in this site by cutting and pasting the following link:
http://www.peachparts.com/shopforum/showthread.php?t=124283&highlight=ml430+battery
I just replaced the battery in my "99 ML 430 with an Iterstate MTP-93. The battery is the same length and width as the original but slightly shorter in height. To compensate for the difference in height I moved the plastic spacer inboard of its original location and it interlocks with the new battery just as it should. This battery is much stronger than the original and is the model Interstate recommends for the ML series. I seriously considered an Optima battery. They don't have comparable power and would be very difficult to safely mount in an ML.
Because of all I have heard and read about electronic/electric problems after a dead battery, or replacement where power is termporarily lost, I went to great lengths to keep power supplied when I took out the old battery. (The original had not yet gone dead.) My post describes the process I used.
Email me if you want additional details. Good luck.
Jim