Some other options:
In addition to an MB battery -
Autozone carries one for the E320 with high CCAs and a good price, about $70 with an 85 month warranty. Great buy.
Interstate makes the MTP-91 - lists for $120 or more. Got one last summer for under $100. Noticeable increase in cranking speed. Satisfied with it so far.
The best Sears, called "International" or something. Also $120 - $130 list.