My 2007 V8 4.2 Supercharged starter motor is struggling to turn the engine over.
I thought the problem was the battery, but the battery is only 18 months old and it has been fully charged and tested where it was purchased and currently has a 98% charge.
I have checked for parasitic current draw, but it is only 30 mA.
When the key is turned to start, the starter motor turns for 2 secs max, stops for 2 secs, it sounds like the battery is dead and then it will turn over again for 2 secs and the engine starts.

Anyone had a similar problem and cure.

I've read that it may either be the solenoid contacts on the starter motor or the engine to chassis earth strap?

Update:- Found an earlier post '3.6 TDV8 starter motor engage delay [Solved]' with the same issue which was solved when the starter motor eventually failed.