2009 Chevrolet Impala Question: AROUND TOWN GOOD-DRIVE 50 MILES SHUT CAR OFF COME BACK 30 MIN LATER BATTERY DEAD

JUMP START DRIVE HOME-AROUND TOWN GOOD ONCE AGAIN DEALER CKS SAYS BATTERY, NO SHORT, NO SLOW DRAIN ALL GOOD CAN'T FIND PROBLEM. CKS EVERYTHING-HAPPENED AGAIN FOLLOWING WEEK DROVE 50 MILES 40 MINUTES LATER DEAD BATTERY- AAA JUMP START- SEENS IF I DRIVE 1 OT EVEN 2 HOURS STRIGHT AND STOP BATTERY IS DEAD ANY SUSJESTION ON WHAT MIGHT BE CAUSING THIS- THANKS