Flooded-cell (wet cell) batteries should stick about
12.60 V after being full charged (with no load on
them) for quite a while.  My new Interstate starting
battery is there two weeks after being charged up with
only the VW clock and the stereo memory on it.

If it drops much or steadily, it a sign of a battery
nearing the end.

For good info on equalizing, see this page at the Trojan
Battery site:
http://www.trojanbattery.com/BatteryMaintenance/Equalizing.aspx
Note their recommendation on when to equalize.  If batteries
are kept fully charged; that is, not left discharged for a
while, and are charged to the correct voltage, they ought to
be fine without equalizing.  When a battery is left in some
state of discharge for a while, or discharged below its recovery
voltage, then maybe equalizing will help.  Maybe it won't.

FWIW--I have four huge Trojan 6V batteries running a PV light
system at a mtn cabin at 10,500' behind Boulder.  These batteries
are 5 and 6 years old.  I haven't tested them this summer, but
last summer they were fine and I expect that's what I'll determine
later this summer when I test them:  fully charge them, and
then disconnect them and let them rest 24+ hours, then
measure the voltage and see how close they are to each other.
These batteries get down to 18 degrees F in January.  Setting
the charge set point (voltage) is the key to keeping them going.
The charge set point is 15.6 V in the winter and 15.0 V in
the summer when they warm up to, say, 50 degrees F.  I never
equalize them.  I can't--my charging system doesn't have such
a setting.  ;-)

Also FWIW--my UB12220 sealed batteries under my driver seat
take a charge and then sit at 13.00 V or just below for a
long time.

There are other pages on the Trojan site with good info.

Richard