My car has a power shortage, what can can it be and how can I fix it?

now I have this problem like 5 times already, for some odd reason, when I leave my headlight on for about 5 to 15 minute without starting the car, my car automatically died, all the power will be gone and the car won't start again, unless if I jump it with another car, my friends told me it could be the battery or the alternator BUT i told it to the auto Zone and they check it and the battery is still good, it has three more year of life in it and the Alternator is also ok and working fine and it doesn't have a problem, so what could cause my car to shut down automatically, I check everything is everything is fine, it doesn't show me anything repair sign on the gauge or instrument. so what could be the problem and like I said, when I jump it with another car, my car start quickly. the last time it happen was last Tuesday, I started my CRV and it start fine but a little slow, so I turn it off to make sure what was the problem and I restarted and turn the key to start slowly and it happen again, all of my CRV power such as Headlight, AC, POWER WINDOW, MOON ROOF, RADIO and everything turn off and it won't work and their is not power, every my alarm won't work so eventually my friend help me jump it and it work again. so I don't know what could it be, I though it was the battery or the Alternator but like the people at the Auto Zone said, they battery and the Alternator is fine, I ask my friend, could it be the starter and he said not its fine, so could it be a shortage from the power supply, such as ECU.