Chemistry, Electricity and Reality do not play well together. They love to start pointing and yelling "Liar! Liar!"
A good quality battery in good condition will not have sandbox shovel and bucket fights. The consistency, and repeatability of charge/discharge SG readings should be impressively equal and stay that way for a long time.
This is why the (excuse me)...
H-Y-D-R-O-M-E-T-E-R (gotta throw out a little bait here)
can act as a polygraph machine.
The battery that has bouts of PMS is not going to live as long as one that consistently smiles at you. Keep using it until it plays possum or you start working for it...