I have been having a hard time starting my 1990 350SDL. It was running fine then all of a sudden i would go to start it and nothing. The engine is turning over but i drain the battery every time i try. The battery is less than a year old. What would cause the battery to lose power. I know a couple of my glow plugs are bad would this have that much effect on the battery though? Does anyone have any ideas what could be causing this.

If you have known issues with the glow plugs, address them before exploring the range of other possibilities unless there is something else obvious wrong, like fuel spilling out or you are out of fuel. And, yes. If there enough bad glow plugs you will find it very difficult to get the car started with a cold block.

Fix the known or obvious problems first. Jim

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Own:
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

Owned:
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)