SLman61

I have a sl500 and today coming home I down shifted into 2 going 50 mph to pass a slow truck.car took off fine when I put it into drive the car shut off and red indicator on left display can on its just a solid red light so I pulled over restarted the car it started right up and drove OK but I noticed battery red light was on.I got home and shut off car and waited 5 min restarted fine but battery light is still on.Car never got hot or acted funny except when it shut off..
Anyone have any ideas?
Thank you in advance