My car fried out two brand new battery !!!

Hi there,
About a month ago, my car stalled when I kept it running idle in a parking lot for about 15min. and could not start it. The battery was bad.

I bought a new one from Advance Auto Parts, the "Silver" made by Autocraft. It worked great for a while, then again it 's dead. I drove up to the store to have them checked the alternator and battery.

After checking they said alternator was still good, so they replaced a new one for me. But two weeks later, I got the same problem with battery, couldnt start, after let the car under snow for two days.

Is anybody knows where's the problem from?:

--Is it because of the battery? (Then which branch of battery is the good choice)

--The Alternator? ( They didn't check it right at the first time?)

--Or is there anything else could cause the problem?? electric leaking or ...something else?

Please help!

Right now I have to jump start it every single time I want to drive the car ...(

Thanks in advance for any help!!!!

Q.