Mind you this was a tractor versus a truck but the basic issue was the same. The old gal would just act as if the battery was non-existant and clamping on the jumper cables along let it fire right up.

It was 2 things to make it more fun. First the battery terminals and posts needed the usual wire bush and tightened up. But then it did it again. This time I lucked out. After a little poking and prodding I got lucky. I was standing back as Meryl gave it a try and I spotted a spark from the cable that ran down to the frame. AHA!

Off came that connection to the frame for the wire brush plus some terminal grease after it was clean. Bolt it back down and it's solid.