If you have updated to 2.3.3 , now you can save alot battery because Green power is now working good. you can try it for free on market, I just tried it on my nexus s and its working perfect, i can easely have an extra day, just checked in battery stat and no longer cell standby over 35-40% and no more google map over 10% (just log out lattitude) and set screen auto or lower brightness ! thats it.