For starters, I would drive to the local parts store and ask if they can test the battery and the altenator while in the vehicle. Try to verify that it is charging the battery. If that checks out OK then check for a parasitic draw. The easiest way I know of is to use a basic 12v test light. Disconnect the negative terminal on the battery. Connect the clamp of the test light to the battery cable, then touch the other to the negative terminal on the battery. If the light is bright, you have a draw on the system. Make sure you have everything turned off when checking. You might have a very faint glow from radio memory. If you have an alarm, you may need to pull the fuses to disable it. Start with that an see what happens. | 
