If you're looking for an additional extended battery (you already have the extended back), you can get a Thunderbolt extended battery real cheap here:
http://www.amazon.com/gp/aw/d/B0055...ag=hawk-future-20&ascsubtag=UUacUvbUpU1703602
Note that the picture in the description does not match the actual battery. But go to the htcpedia.com Site and look at the Rezound extended battery options and you'll see that the Thunderbolt extended battery fits just fine in the Rezound and has the exact same model number that is listed in the Amazon link. Mnfg Part #: 35H00149-01M
http://shop.htcpedia.com/htc-thunderbolt-rezound-oem-2750mah-extended-battery.html
And yes, the Thunderbolt extended battery works perfectly fine in the Rezound. Here is my video proving it:
https://www.youtube.com/watch?v=ikSJgbn5D6Y&feature=youtube_gdata_player
Sent from my ADR6425LVW using Tapatalk 2
http://www.amazon.com/gp/aw/d/B0055...ag=hawk-future-20&ascsubtag=UUacUvbUpU1703602
Note that the picture in the description does not match the actual battery. But go to the htcpedia.com Site and look at the Rezound extended battery options and you'll see that the Thunderbolt extended battery fits just fine in the Rezound and has the exact same model number that is listed in the Amazon link. Mnfg Part #: 35H00149-01M
http://shop.htcpedia.com/htc-thunderbolt-rezound-oem-2750mah-extended-battery.html
And yes, the Thunderbolt extended battery works perfectly fine in the Rezound. Here is my video proving it:
https://www.youtube.com/watch?v=ikSJgbn5D6Y&feature=youtube_gdata_player
Sent from my ADR6425LVW using Tapatalk 2