See how to replace the battery in your 2011 - 2016 Ford Flex key fob keyless entry remote.PART # M3N5WY8609 - Order Here:
Then If you have a volt meter try connecting it to the battery and see what the voltage is without turning the key. It should be no less than 12 volts without the engine running. When you try to start it the voltage shouldn't drop much with a good, new, battery. If it drops considerably then it is either flat or a duffer.
Keyless ignition, backup key blade & alt. starting/lock procedures if key fob is dead Since there were a few recent threads about the keyless ignition, the backup physical key blade in the key fob, and what happens when the battery in the key fob dies I went out earlier tonight to take some pictures and put them in one thread.
Range estimated based on Government of Canada approved test methods. The key fob uses one coin-type three-volt lithium battery. For instructions on how to replace the battery in the key fob, refer to your Owner's Manual under Keys and Remote Control.Notes: Do not wipe off any grease on the battery terminals or on the back surface.