I had loads of issues with my 6R on a 60plate & original battery. Car going flat randomly, brought engine warning lights, with various errors recorded too. All it turned out to be was my battery was running at about 40%. Sometimes it worked on start up and sometimes it never, even after a good run out it would sometimes fail after leaving it a few hours. Sometimes work after 2 days leaving the car!. I paniced as the symptoms didn't sound like battery issue, and that something was draining it. New battery on and was fine.