I bought this Chinese battery from the maker, Andida, from this seller on ebay- about 3 months ago...
http://cgi.ebay.com/2000mah-Spare-Ba...item5ad83f1369
for $9.99- it is 2000mah- no special cover needed.
I have a Sprint Touch Pro 2...stock rom... battery can last me all day with normal use- surf the net, make call, constant texting.... so I charge it once per day.
I had to charge my phone 3 times a day with the OEM battery 1500 mah...
Also helps that I have some apps helping as well...like Glight...
Just my 2cents...