Chosen Solution
how do I dispose of the old battery pack?
Once or twice a year there are collections for hazardous materials. If the next collection isn’t coming up soon, take it to the Apple store and they will recycle it properly. You should be able to find the dates for these pickups on your towns website. (most towns have websites just look up the name of your town online and you should be able to find it) If there is a recycling center nearby you should be able to take it there as well, just remember to read their guidelines on what they accept.
The best way it to find a local recycle center near you. If you have a local Apple Store just drop it off with them. I would just leave it on the counter if they give you a hard time ;-}