I have the Seidio 3500mAh extended battery. It adds bulk to the phone, but actually I find it actually makes it a little easier to hold, but that's just my opinion. I recently just started using it again. Right now I'm using Albinoman's Beta 3 Jellybean Rom, and with moderate usage I'm getting around 2 or so days with it. The battery life is okay on the ROM, but I want to say back on Cyanogenmod 7 I was going like 2 or so days with heavy usage (wifi tethering for a few hours and playing games for a few hours each day) so it just depends on the ROM and your usage, but I'd say 2 day minimum.