If your battery is not holding charge check the following:

Faulty Battery:

Check battery water level, if low fill battery with distilled water.

Load test battery, if battery does not past the first test. Charge the battery for 6 to 8 hours and retry. If the battery fails the second test. Replace battery. 

Check for battery drain.

Check if alternator is charging, charge should be between 13.5V to 15.5V.