Honestly, if they were taken out of vehicles, they most likely are end of usable life or at least very near to end of life.
Charge one for 24 hrs, then remove the charger and let it rest for one day.
Then put a volt meter on the terminals, if it registers anything less than 12.8V it IS TOAST.
Personally car (and especially USED) batteries are not all that useful for boondocking.. That is when you are WANTING a GOOD deepcycle AND max capacity you can get per pound.
Take a couple of the used batteries to your local battery place, use them for CORES and get some NEW batteries..
Your back will thank you for not dragging a half dozen partially dead batteries around for a long weekend camp..