Why don't keys lock and unlock doors anymore?

You need to visit an auto electrician, an alarm installer or an auto locksmith. The key fob needs re-pairing to the locking system.

Videos that might help

https://www.google.com/search?q=2012+Dodge+Charger.+Key+fob+not+locking+and+unlocking+doors+after+battery+change

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Replace the battery on the key fob! Also, it may need to be reprogrammed by the Dealer!
Dr. Gene n Landrum

try powdered graphite lock lube for the keyhole if it does not get easier, there is a mechanical obstruction in the door.

these fobs are of poor quality have you tried replacing the battery?

Pull the switch panel and verify you have power to the panel first.

lock driver door then passenger door with the key wait 5 mins then unlock the driver door with key and then passenger door with key but don't open the doors when you first unlock it then after all doors un lock then hold foot on brake then insert key turn it to on position while holding brake down
then release brake then compress brake 3 times and then turn the key to off position. this should reset the security system for you

Give some more details of the problem.

Programming
When
Key added or replaced. System malfunction.
How
Obtain all keys. A maximum of 3 keys can be programmed. Close all doors and boot/tailgate. Switch ignition ON. Repeat procedure below 3 times: Within 4 seconds: Press key lock or unlock button. Within 4 seconds: Switch ignition OFF. Within 4 seconds: Switch ignition ON. Within 4 seconds: Press key lock or unlock button. System should now lock or unlock vehicle. Within 4 seconds: Press key lock or unlock button. Within 10 seconds: Press lock or unlock button of first key. System should now lock or unlock vehicle. Press lock or unlock button of second key. System should now lock or unlock vehicle. Press lock or unlock button of third key. System should now lock or unlock vehicle. Switch ignition OFF. Remove key. Check operation of all programmed keys.
NOTE: If less than 3 keys are to be programmed, remove ignition key after programming last key.

1. Driver's doo opend and unlocked, all other doors closed and locked
2. Inser Your key in ignition, don not turn, remove key
3. using the manual lock/unlock button on ther dirvers door, slowly press lock and unlock 5 times (count the lock 5 times and unlock 5 times)
4. Shut door
5 Open door
6. Using the lock/unlock button on the direvers door, slowly press and unlock 5 times (count the lock 5 times and the unlock 5 times)
7. With the door open insert you key into the ignition, turn to ON position (don't start), wait 5 seconds. Trun off and remove key.
8. Locks should cycle once (Car will lock and unlock once). If they don't cycle or they cycle more that once, do stips 1-7 over.
9. Using the remote, push lock button, hold for 1 second, release. The locks should cycle once. If not start over and go slower.
10 Close the door. Open the door. Press the lock button on the remote. The locks should cycle. Close the door. Press the lock button on the remote, the doors should lock. Press again and the doors shoud unlock.

I got this from a site called FixYa (don't have URL). It took me a few tries but it worked like a charm.

Here you go.If you can't read it I can email it to you.