96 cummins, auto, 4wd, 165k, 6" stacks, pump turned up.

For the past few months even before it got real cold I've been getting the occasional dead batteries, at least that's what its acting like any way. Most of the time I can jump it and it'll fire right up. But there's been a few times it took me a couple hours to get it going. Today at work I had to hook it up to 2 fork trucks that have 2 batteries each for 30 minutes to get it to fire. before all I got was a slow crank or two.

I've done checked all the grounds and done a search online but nothing is as intermittent as what I've got.

Any ideas
Batteries tested good about 2 months ago.

 

Sounds like at least one battery has a poor cell. Have the batteries rechecked and load tested.

 

if the batteries are good you're gonna want to do a parasitic draw test

 

it might be the alternator wire to turn it on mine was doing that same thing i ran a switch from alternator to battery eveytime you get out or you know your gunna be awhile till your back to start truck shut it off so the alternator wont draw power hope this helps

 

I've seen a bad alternator suck the life out of a battery.