A battery can have an intermittent open circuit caused by a problem inside the battery. It will start and run ok and they die having no power whatsoever. Then later it may start fine. If I were u I'd borrow a battery from someone and run the car for a while, if it doesn't die you know what the problem is... the battery. It is impossible to say for sure considering the vaugeness of the internet and me not knowing your experience level. Try another battery.
STIMPY21