How to do battery charging cycles?

My phone has 100% when I walk out the door, and during school I use to to text and use the Internet a little bit; it isn't much and the school has Wi-Fi but by half way through the day I have half the battery! How do I perform therapy or whatever? That battery charging cycles and stuff? IPhone btw

Added (1). It's an iPhone 3GS! Maybe ill get a mophie!

That's a typical smartphone. Battery isn't meant to last that long.

Is it new? Or older model? If it's at least a year old, the battery probably lost 10-40% capacity.

Doesn't matter if you cycle the battery or not. The battery won't really last more than one day unless you don't use it