iPhone 4 Battery suddenly decreases very fast / iPhone won't turn off

Hi fellow apple fans!

My iPhone 4 its battery life has decreased dramatic, since one month or so.

Without doing anything, having location services turned off and brightness at 50% it goes down with at least 6% per hour.

Furthermore, the iPhone cannot be turned off. If I turn the phone off, it restarts automatically. It does this every time.

I did a reset and restore already, but no luck so far. Anyone who has an idea? I hear more people with batterylife problems since 5.1.