Did you update any app recently,
did you turn off any background services that are not needed,
did you add any apps with live tiles,
You really do not need a battery app because they can only run every 30 minutes from what I have been told. Best way pin settings to start screen, then scroll down to battery.
Those are good tips.
There are some other things that can be done as well to help keep your battery juiced such as...
keeping the screen timeout low
disable backup options
disable Xbox live if you don't play Xbox live games online
Turn off "Connect with Xbox music and the cloud connection
Turn off feedback
Turn off keyboard feedback
Sync e-mail manually or increase time between automatic e-mail syncs/checks
Disable automatic SkyDrive Upload
I'm sure that there are many more tricks a person can use to help preserve battery life. Those are just some of the few I've heard about and tried that have helped me out.
And as Corepc wrote, you really don't need a seperate battery app, but if you still want one or a battery/utility app, I suggest giving "Insider" by DAONE a look. It is a very well designed and executed app with many features. I have found it to be the best all-in-one type utility app in the market.