Ford 2009 Flex Owner's Manual page 316

Roadside Emergencies
3. Once the disabled vehicle has been started, run both engines for an
additional three minutes before disconnecting the jumper cables.
Removing the jumper cables
Remove the jumper cables in the reverse order that they were
connected.
1. Remove the jumper cable from the ground metal surface.
Note: In the illustrations, lightning bolts are used to designate the
assisting (boosting) battery.
2. Remove the jumper cable on the negative (-) connection of the
booster vehicle's battery.
316
2009 Flex (471)
Owners Guide, 2nd Printing
USA (fus)