Actually, it was this person who sold them this summer too.
All you need to do is pop the back of your android screen off after unscrewing the screws under the pads, unplug old battery, plug in new battery. The batteries should be good from this guy as if the screen doesn't work it's not being used a lot. Just expect the battery you order to be dead, but it holds a charge and has worked great thus far.
Otherwise, I do not think there's a place to order just the batteries...I checked every where I could this summer.