I know many people don't want to spend 90 bucks on a battery, but I bought one like this on sale for 60 bucks and it has been worth every penny... Plus I like the look and feel of the extended battery door they offer better than the other cheaper ones.
MUGEN POWER 3600mAh EXTENDED BATTERY SAMSUNG GALAXY S II EPIC TOUCH 4G ACCESSORY | eBay
I can literally get 48 hours of moderate usage in a poor signal area (work). Best extended battery I have ever used...
The same company has a slim 1950 extended battery which uses the same battery door as the original, but I don't have it and can not comment on its life.....
MUGEN POWER 1950mAh EXTENDED BATTERY SAMSUNG GALAXY S II 2 EPIC TOUCH 4G D710 | eBay
These are obviously much more expensive than the many options under $20... But the fact that they're flat is a pretty big selling point, to me. Seriously, battery makers, I appreciate the bigness, but I don't want my phone to have a ed bump in the middle.
Anybody know a place I can get a reasonably-priced flat-backed battery/cover?