Well ... my "they are like new" original 200 amp hours worth of eight year old AGM coach battery bank comments are based on:
THEY CAN STILL (as of this past February) - run the furnace (within it's ON/OFF cycles) two or three nights, along with my CPAP unit those same nights, along with the cooktop fan several minutes those days, along with the bathroom fan a few minutes those days, along with the smoke/propane/CO detectors those days/nights, along with the refrigerator's control circuit board those days/nights, along with the LED lights those nights, along with the roof vent's Fantastic Fan several minutes (within it's ON/OFF cycles) those days, along with start the Onan generator a few times, and along with operating the laptop computer (using it's special 12 volt brick instead of a wasteful inverter) a few hours those nights - THE SAME AS I expected of these batteries when they were new.
Granted they may not have their full capacity left, but it sure seems like what capacity they have left is good enough so as to not need a full-blown load test or rocket science instrumentation to prove it. :h