Came back to my car (2008 is250 SEL) last night after a meal out, but the car wouldn't start, strange thing was, had the green light on the ignition button, but nothing else, managed to jump start it and get it home, tried it this morning and it started no problem, should I replace the battery? Or is it an alternator problem? I replaced the battery when I first got the car, that was just under 3 years ago, I still have 1 month left on the guarantee on this particular battery, so not sure whether to just get it replaced? Thanks