So I bought a new battery because my n810 wasn't constantly recharging (any time I tried to recharge it, it went into a recharging loop where it'd recharge a little, reboot, recharge a little, reboot, etc. until it stopped recharging). I bought a replacement battery and installed it and now it seems to be charging very well.

Anyone know where to send the old (dead, swollen even(!)) battery?

Hmm. I've poked around more and found http://www.nokiausa.com/get-support-...ecycle/recycle

It looks like this is where to send old Nokia-branded stuff, including batteries, to get recycled.

http://www.nokiausa.com/get-support-...hone/batteries
http://www.nokiausa.com/about-nokia/...how-to-recycle

It's postage-paid, so it's free to you, and there's no excuse for not living with a clear conscience about dumping bad things (here, Li-poly batteries) into the landfill.

Of course, if you have an n900, n810, n800 or n770 and it still works, you could recycle it by sending it to me.

Call up some local electronics stores and ask if they are participating in battery recycling programs...

A nice link to help verify that the battery is really a Nokia battery:
http://www.nokiausa.com/urgent-redirects/battery-check

(Probably want to check this before you send them "their" battery for recycling, so you don't get stuck with the bill!)