My guess is that most people just toss it so you may not get many responses on discarding it.
You should take it to a recycling place that takes batteries, but there may not be one in your area. Call your local hobby store and see if you can drop it off there. They may just throw it away anyway, but at least you have a clear conscience

As far as discharging to zero, I think that may be dangerous and inviting a fire. That may be nimh tech, not sure. I'm sure people will chime in on that part of it.