I bought a new 1980 300D when they came out, and it would not start worth a darn below 0f. I just let it run all night. The batteries that came with the cars when purchased just were not as good as today's batteries.

I just bought a new Interstate Battery (for my 1983 240D)that I want to highlight. It is called the MEGA-TRON PLUS 93 (Interstate Product ID MTP-93), and it is a mega-tron. When first installed, I turned the key, and my warning buzzer about blew me into the back seat. It was probably 3 times louder. The battery has 1000 amps and 850 cold cranking amps. If there is a better one, let me know.

Firestone sells the battery for about $129 + installation (Chicago area). They sell it as the MT-93 on their books (don't know what cars it fits, but check before you buy). Here is the link with info:

http://www.interstatebatteries.com/cs_eStore/Content.aspx?dsNav=Arpp~12,A~Part+Number,N~21-2147384761-4294490516-4294492617-2147384903,Nr~AND(P_unique_id%3aMTP-93%7cMercedes-Benz_240D%7c1983_Standard+Battery_L4%2f2.4L)

will not start
will not turn over