Why Do I Have Horrible iPhone 5 Battery Life?

When I first got my iphone 5 in September my battery was great. But when I upgraded to ios 7 it started to go bad. It drains quickly, the battery percentage jumps around (for example my phone was on 40% and I Facetimed someone and as soon as they answered I looked at my percentage and it had dropped to 23%, in a matter of seconds.), it also dies around 15 percent. It sometimes varies when it dies though. Sometimes it will die at 10% or 11% or 5% but mostly dies at 15%.It never goes to 1% like it used too. Is there anyway I can fix this?

"iPhone 5, ios 7". That is all the reason you need. You chose the wrong phone & don't know how to manage it.