Pull the pos of the battery one night and then reconnect it when you go to start it in the AM. this will tell you if the battery is bad. Actually the easiest thing would be to take it to an auto-parts store that has a tester, they normally take the tester out to your car and check the batt, alt, and diodes all for free.
Don't forget to Search first then ask questions later! The loose nut behind the wheel