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

I am finding I have to adjust the pot for each battery. 14.7 on the one yesterday was 14.54 on the one today.

It was a surprise to me that I had to do that, and I wondered why I had not seem anyone mention it anywhere.

Akso some of them, the voltage settles within in a half hour and some it keeps rising for 2 hours.

That caught me out, on the first battery! Resulted in it being at 15.24 for maybe ah hour or more. OTOH that battery looks the best tiday, sitting at 13.09 after several days' rest