Got my new (used) batteries!! Now, how do I rejuvenate them?

Those are 1/4-20 or 1/4-28 machine thread,
Goto the hard ware store and get some get the stainless steel version if they have them, less likely to corrode
about one inch or so
Stack your cables on top of each other, see how thick your connections will be
And try to go at least 1/2 inch longer
I forget how deep the thread goes
Use a nail or paper clip or drinking straw to measure how deep the holes are
You want a good bite/grip with the bolt, but you don't want it to bottom out and have loose cable ends