Most likely the battery, check the water level, if low fill with distilled water and put on a charge, if the car dosent start after a good charge, or a quick jump pack then your starter might be wired wrong. I know it sounds weird, but if wired wrong it can start and run but will drain the battery. Also if it does start put a multi meter on the post of the battery and see if the voltage is around 13.50 to 14.00, if you get that voltage output you have an good alternator.Also might be main relay. I need to puts my thinkin cap on