Easy Battery Saver - See
here
That was the best battery app I've ever used and it actually works amazingly well. On my SGS2, with the stock battery, after installing / customizing this app, I got around 3 days from 100% battery to 10%.. and this was not just a one time event. I've tried this app for close to a month now.
Check it out. It's really worth it. Very easy to use and customize.
PS., and no, I'm not involved with this app in any way other than being just a user and so I'm not trying to market this app.