I bought the XA-11 from Amazon, and two extra batteries from B&H. Now, one of those three will not hold a charge. I have labeled my batteries, but I don't know if I have ever used this particular one.
In the charger, it starts yellow for a moment, and switches to green, but in the camera, it shows no charge and will not power anything.
Do I have a lemon battery?
This may be the battery that was included with the camera originally.
If I'm S-O-L, then what's the best way to dispose of a LI battery?
Sounds like the battery is bad since it fails to hold a charge. For disposal, you'll need to look for a local electronics waste location. Sometimes hardware stores also allow for battery recyling, but check to see if they would allow these larger types of consumer electronics batteries (they may only allow for AA, AAA, etc.)
As to why the battery is bad, a complete guess as to whether it was a bad part from the beginning. However, purchasing from Amazon could have led to you having a gray market or counterfeit battery. For the future, purchase your electronics from reputable dealers only (e.g. B&H, Adorama) or of course directly from Canon.