Thanks guys. I think I try to finish out this season then replace it next year. I might even do what I do with the old Pontiac's battery. Every winter, it stays disconnected and hooked to a charger that is on a wall timer set to come on for 1 hour a day.
Charge fully overnight then start. Measure battery voltage while running.
I fully charged it last weekend when it wouldn't start and tested when running at 14.1v
If you don't keep a maintainer on it over the winter, 1-2 years is typical. With a maintainer, 3-5 years is attainable.
I don't use a maintainer but do charge the battery once a month during the winter. The mower was stored in my workshop which never drops below 40 degrees
12.3v and barely starting the motor? Sounds like your losing a cell. What brand?
It says MTD products, made in USA, no other name.
I think another cause of short life is the vibration a mower battery receives.
My yard is one acre and pretty rough. My wife also took care of the next door neighbor's acre so it could have been beaten to death.