Battery questions are hard to answer. Mine are on their last legs and I can play around for most of the day. We have a large hill separating our property and this is where the battery gives up the ghost. The "Curtis" fuel gauge suddenly stopped functioning and I must address that.
How long batteries last depends on usage and maintenance. I bought mine at an auction cheap, but bought new plastic and OEM seats.
The downside is that JD thinks they have a license to STEAL on all things TURF! I just paid $30.00 for a $3.00 Motor Bearing, not knowing it wasn't anything special.
An electric Motor is a few grand, as is the tranny. Same for the controller.
Yesterday, I think I broke an axle shaft. Electric vehicles have tremendous torque and at 4000 something hours, I guess the shaft just had enough. Fortunately, I had bought an entire used drivetrain and controller for $500.00 some time ago. I will just switch out the whole motor/axle assembly. I really, really miss that machine when it's not in service.