I have noticed that my Sport will crank like the battery is low at times. It just seems sluggish. It has never not started. I wonder if low voltage is causing this issue. On some of the older Bosch injected cars if the voltage dropped a little below 12 volts the car would NOT start. It would crank all day without firing. My Alfa Romeo 164S had a (no kidding) truck and bus battery to keep this from happening. If you cheaped out and put a crappy small battery in you would be hit and miss on starting success.
Our batteries don't look as though they are the best of quality. I have been thinking about just going ahead and replacing the OE batt with an optima one.
Just some thoughts.