Having the battery checked is no garanty that is is good. Checking is done by drawing a lot of current in a small time to see if the voltage drops. If the battery has an internal shortage it may test as good but lose its charge in one or two days. The best way to test it is to charge it to full capacity with a battery charger (check the water/acid level first) and see if it holds its charge.
And of course test with an amp meter for power leaks. It can be something as simple as a trunk licht that stays on.