Help! Slow Battery Discharge

I donoo, I have an 86, 98 Ranger, and a 95 Olds. One of those routinely sits for more than 2 weeks at a time, like this summer. I was driving the 67!!!! Never had a battery go down.

One of these days, when I have nothing else to do LOL I'll measure the drain on all of 'em and see where we stand.