service charging system blues

[CP MUSTANG 07]

My 2007 V6 has been giving me fits lately. I drive my car daily and have clocked 70k+. I had the original alternator go south early last year...replaced under extended warranty. Then the thermostadt housing (PLASTIC!) cracked liberaly spraying coolant through the engine area! Again under warranty but down time on vehichcle for parts. Since then I get service charging system warnings which appear then vanish....its broke...its not broke...oh its broke again! Dealer could not track problem as it never indicated while at the shop...finally used ipod nano camera to prove. Finally dealer said we will replace the alternator ( maybe its going...they dont seem to last). Well new alternator...problem solved....oh its back. The system check list shows all is well....then the on and off warning for service. The battery shows 13+ volts engine off and 14+ when running so battery alt seem to be ok. Could the computer have a defect sending false indications? Any V6 owners out there come across this gremlin yet? Love the Mustang but these warnings are pissing me off