When you say you keep burning it out, what do you mean? What are the symptoms that lead you to think it is burned out? Does it literally burn, or what is the failure mode? Stops charging? Battery dies? Starts squealing and siezes?
Do you rebuild it and put it back in or do you buy a new one and install that followed by another failure? Is the failure mode the second time and third time the same?
The problem diagnosis will be more successful if you give us some additional data. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)