I got 6 years out of the battery on my Ztrak. Its a entry level commercial mower, used in a residential setting. I got about 300 hours out of it roughly, stored in a non heated garage in the winter, connected with no battery tender.
Never had an issue, until the day a cell went bad and nogo.
I have always wondered about the rough conditions of mowing and the vibration. Hasn't seemed to be an issue.
My last JD commercial mower used the same battery as a late 90s early 00s honda civic. No issues with those as well.