The vehicle has a battery saver feature designed to protect the vehicle's battery.
When any interior lamp is left on and the ignition is turned off, the battery rundown protection system automatically turns the lamp off after 20 minutes.
This prevents draining of the battery.
Chevrolet Cobalt Service & Repair Manual. Battery Cable, Replace
Ground Cable
Battery To Battery Tray
Caution: Unless directed otherwise,
the ignition and start switch must be in the OFF or LOCK position, and all
electrical loads must be OFF before servicing any electrical component.
Disconnect the battery ground to prevent an electrical spar ...