I had this problem: my car randomly wouldn't start. No crank, no switch sound, nothing when I hit the button. Completely occasional and random. Yet the battery was charged. I checked and cleaned the terminals (but not the ground - D'oh), all to no avail. Finally, I made a hard foam shim as I noticed that the battery had a half inch to slide forwards and backwards in its tray during acceleration and braking. Haven't had a problem since.
This is about as scientific as Gatorade, but it seems to have solved whatever problem I was having.