I found another cool baseball gadget. It's the Virtual Speed Baseball. According to the blurb, it will show you the speed of your pitches and has a battery life of 100,000 pitches. If you figure an average of about 100 pitches per game, that's about a thousand games. So it should last a good long time in practice.
Warning, the ball is NOT meant to be hit with a bat, just for pitching practice.