Since this cold spell we are having, I had the same problem. Battery was NOT the issue....worn brushes on the voltage regulator was the culprit. Check your voltage regulator...very easy to do, just two scews hold it on the back of the alternator and it pops out. If the brushes are less than 1/4 inch long or so, you are not getting a full charge. Simple $20 replacement. Also, my Interstate battery was way low on electrolyte. Topped it off and made a big difference also.

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"Life is tough...it's even tougher if you're stupid." John Wayne


Dave
Pawleys Island, SC

'79 300CD

I had to replace mine yesterday. Went back to Autozone with the group 49 I bought from them 12/2005 . . . it tested bad and their 7 year prorated warranty gave me back $35. They had a fresh 49 on the shelf for $94.99, done and done. 5 years on a battery in my MB diesel in Colorado seems pretty good to me, and $35 off a new one is icing on the cake!

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1981 300D - {172,000}
1971 220D {Sold to TomJ}