Hi nothing will throw up stop/start problems more than a bad battery also the stop start won't work if you have the aircon on, a bad battery will cause all sorts of weird problems as these vehicles rely heavily on voltage continuity, sluggish is the last gasp before you start getting Can gateway problems, bet if you plugged it in there would be a few low voltage faults, don't know what milage you have but I never replaced my starter in over 200,000 miles, mind you I never used the stop/start as it knackers you r flywheel and ring gear. Steve.