Battery giving me problems?

I just had an alarm installed on my car yesterday. Since this morning I have gotten in and out of the car about 4 different times. Each time I go to start the van up, it will not start. There is no power anywhere. I open the hood and wiggle the battery just a little, and the van starts right up. This has been happening all day. The battery is not corroded and the bolts are tight also. What could be the problem?