My 2001 F350 Super Duty diesel keeps draining my batteries for some reason, wouldn't crank on Friday. Put my battery charger on for a few hours and it started fine. The rest of the day fired up fine, on Saturday it happened again. Had both batteries charged and load tested today, they are good. Short???

 

Are the batteries low on Water? short wold blow a fuse. Could be something pulling a load with the truck off.

 

Hi,
Saw this!

 

with the engine cool, feel the alternator. if it is warm one of the diodes inside is burned out and the alternator needs to be changed.

 

You can use this method also. Just make sure you don't have anything else tied to the other battery since you have two, or disconnect the other battery. The idea is to make sure any drain goes through the testlight, not around it through the other battery.