I wonder if there is a charity that could place it in the hands of someone who, like your father, could use the extra mobility.

As for sales, it is my impression of the used market for all battery-powered items (anything from golf carts to hand drills, or roombas) that the unit with a dead battery is a challenge to sell- people already know the cost of the replacement battery and seem more comfortable purchasing an entirely new unit than used. In the case of hand-drills, the price of a new battery is often 2/3 the cost of a new unit (with a new battery!).

Ah well- it's always a trade-off. Good luck! I hope it finds a good home.