I have the OEM extended battery (and back) from Verizon as well as a 2nd standard Samsung battery (with separate base charger) I bought on Ebay. The extended battery adds bulk, makes the phone heavier, but does last. What I prefer to do is to use the regular battery in the phone, while the other "extra regular battery" stays charging at home. I turn the phone on at 6am, go to work and change batteries when I get home a 6pm. Since I rooted and put on EB01 (now EC01/ED01 Froyo), use SetCPU and the Brightness Level apps, I never get close to running below 30%, unless I'm in a building that inhibits good reception and the phone's radio has to work extra hard to get a signal
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