or just buy the 2000Mah extended battery that is the same size as regular(stock) 1500Mah and does not require different back nor does it add any weight(ebay for $10 includes shipping). I got this one a while ago:
http://cgi.ebay.com/2000mah-Spare-Ba...ht_2704wt_1137
Its a genuine Andida battery but i didnt get it from this seller(dont remember my seller since it was about 6 month ago) - so make sure you check before you order(there are a lot of fake ones)