2003 Toyota 4Runner Not starting some time.

I have aToyota 4-Runner 2003, 6 cylinders. Renecntly, it has started needing jump start some times, thereafter the battery is good for a few days. The battery itself is less than 2 years old. I have got the battery checked at the Auto Zone; they say that it is good. When I turn the ignition key to start, it will just click and will start right away with the jump and works fine for days until it happens again the same thing.
Are there any relays involved? The alternator is charging all right.