my friends 06 600 SDI was experiencing difficulties, seemed like it was dropping a cylinder and running rough at idle and when you hit the gas it bogged bad. a new battery fixed him right up, runs perfect now.
on a side note, the SDI feels like it has flat spots when you turn the clutch by hand, gives the same feeling as a crank bearing going bad. this is due to the much larger stator and flywheel, the magnets cause this feeling in the motor. i found this out after tearing the motor out and down thursday night!

well a new base gasket, set of rings and a couple circlips and it went back together last night, three hours from completely stripped to running

3200 miles on his SDI and the pistons looked like new, i was very surprised with the lack of wear on this motor.