I've read alot (probiably not all though) posts about battery life and things to save it etc etc, but my battery life is still pretty dismal. I know you have the HTC battery extended battery which is 1500 mah and the other HTC battery which is 2150 mah and you need a new back cover. I've also seen the Seidio 1750 and 3500 batteries. Are the 1500 and the 1750 worth getting, or step right to the 2150 or the 3500? Reason I ask is I'd like to keep the existing case I have ultimately the phone has to last all day.