After charging battery theft system light on

Electrical problem
2005 Buick Terraza 6 cyl Two Wheel Drive Automatic 28k miles

28k miles, left the dvd player on overnight and battery went cold dead, slow charged the battery for 12 hours, was careful, positive first negative last and reversed when takeing cables from charger off.

now the "theft system service required" comes on in the information display when starting, and a red warning light stays on in the instrument gauges.

how to turn it off? Not worried about van getting stolin lol

mike

thank you