I would like to share my experience of battery purchase. I bought a battery from ebay, this one:
I recieved the package in just over a week, but it was a battery for some ZTE device!!! I contacted the seller and they immediately sent me another one. Under one week later I had my new battery(seems like an original battery).
On first charge it seems to hold a lot better then my 15 months old battery I had. Charging now takes 1.5 hours like it used to, the old battery was 0-100% charged in 30-40 minutes, with the original charger.
So for 4.99$ or in my case under 4€ including shipment I can go more then a day of normal use, surfing, mail, calling, reading xda..
Or easily 2 days of light use.
I think it was well spent money, I recommend!
Edit: I guess I should mention that battery tested with ezet CM7.