Hi
A bad terminal connection would cause it
only way to no for sure is put a multimeter on it and see what current drain is on there, then you can work out how long the battery will last
also if you car is going to sit for more than two weeks, I'd get a trickle charger for it, the electronics on these now days will drain a battery over a period of 2 to 3 weeks
I bought a Jaguar one, but CTEK make the exact same unit for half the price
cheers
Joe