My battery life has been totally awesome until I started having the Facebook lockup issue a few days ago. That seems to be dinging my battery life a little bit, but it's still solid. Sometimes I even forget to charge it at night and there's plenty of battery to get me to work the next day.
I had lower battery performnace when I first got this phone. It takes a few charges for the battery to hold a better charge. Enabling the pawer savings mode helps. Disbaling some of the sync features on your google account can also help. There is also a good day of sync that goes on when you first set up this phone if you use an common smart phone features.
I've diabled the Sprint Connections Optimizer as well, I found this to have a HUGE drain on battery life rather than helping.
After a few chargers, it does get better. However, using the power saving mode makes the screen way too dark. I'm still going to purchase an extended battery when it comes out. This phones still burns through battery faster when you use it. I guess I'm more disappointed since battery life was touted as being much better; a feature highlight.
I use JuiceDefender Ultimate and I get at least 24 hours out of a single charge. I'm on my phone contantly (texting, calls, FB, my 4yr old daughter plays with apps) and I think there was 1 time I made it 18 hours and my battery got underneath 18%. I think this phone's battery blows any other phone's battery out of the water! My boyfriend got jealous because my batter lasted longer than his iPhone battery lol.
There are several out right now, you can check amazon.com for choices. Although I haven't purchased it myself, there is a combination case/extra battery also at amazon. What someone needs to develop is a case with a holster that acts as an external battery that way every time you put it in the holster it will recharge or "top off". This is feasible now since lithium batteries do not suffer from the dreaded memory effect.
Check out a fun infographic that teaches you how to increase storage, enhance security, improve battery life and clean your device.