Doesn't sta back up after driving.Has 2 new batteries.Cranks,won't turn over. on 1995 Ford F-350

Drove the truck for almost a year with only one battery and no probs.Took a road trip and turned it off after 400miles and it would not start.Cranks, but won't turn over.Bought one new batteriy and it cranked fine but if it sits for a day or 2 the battery is dead.Bought a new 2nd battery today.Cranked right up, drove for 20mins,tried to crank again same thing. Cranks, won't turn can crank it by spraying air cleaner in the air filter.Bought a new air filter today, but it's still doing the same thing.Electrical???

by in Daytona Beach, FL on October 10, 2012
1 answer
ANSWER by on October 10, 2012
check your alternator output should be between 13.8 and 14.2v