You'll probably see more replies advising you to clear your cache partition, as well as other ideas. But I have discovered that when my battery has a bad day, the first thing I do is simply pull the battery. Don't turn the phone off; just remove the back and then the battery, give it about 30 seconds and re-install the battery and power up the phone. The vast majority of the time this fixes whatever is going on. If you've recently installed a new app or two, you might consider uninstalling them and seeing if that helps. This is generally how I proceed, for starters; then moving along to other methods of troubleshooting. Good luck.
Edit: I forgot to ask: Has this been going on for a while, or did it recently start?