I found this pretty interesting: a 1850mah and no BIGGER cover needed battery from Andida, ordered it from ebay for only 24 buck shipped i will make a review after fully tested it!
link: Samsung Google Nexus S i9020 Highcap battery 1850mAh - eBay (item 230612298632 end time May-21-11 16:21:39 PDT)
link: Samsung Google Nexus S i9020 Highcap battery 1850mAh - eBay (item 230612298632 end time May-21-11 16:21:39 PDT)