Hi, welcome to JustAnswer!. This is Ed.
That was some nice work! But just to prove that no good deed goes unpunished... apparently your immobilizer forgot the key code.
The theft system you're battling now is the Sentry Key Immobilizer System (we call it SKIM) and its only job is to decide if you can go for a ride, depending on how it feels about the key in use. The first few times you try starting the car with an unacceptable key, you'll get that start-die phenomenon, but eventually it becomes irritated and that's that. No starter.
The only two possibilities are that your key became damaged somehow and the RFID transmitter chip isn't working, or the SKIM unit has forgotten that it and your key have been introduced and worked together at one time during the battery disconnect. It's not something I would expect to happen -- quite the contrary, you should have been quite safe -- but weird things do happen during power outages. Add this to the list.
Your options are to gather up two other working keys in order to do your own programming of the third key. By using two keys that still work, it proves to the SKIM unit that you really are the legal owner, so it'll let you program a third key without going to the dealer. To do this, insert each working key into the ignition, roll it ON, wait 5 seconds, then remove the key and insert the 2nd working key. Repeat. Then insert the non-working one and the electronic handshake will take place, adding the third one to the list of working keys. You can do up to five more this way.
But I have the feeling you may not have all these extra $100 keys just lying around. That means we'll need some luck or a trip to the dealer.
I'd try another battery disconnect, but this time, have the key already in the ignition and have the key on. Perform a complete capacitive discharge of the electrical system by touching the battery cable ends together for 4-5 minutes, then reconnect and see what happens. If this works, I'll be as surprised as you (I'm totally making this up as we go).
The only sure thing (if such a thing exists) is to have someone with a capable scan tool come to the car or have the car go to the scan tool. A mobile locksmith is one such resource if you'd rather avoid a tow bill. A special 4-digit PIN will be requested during the process, after which the key should be back in the fold and all will be right again. PINs can be obtained from any Chrysler/ Dodge/ Jeep/ Ram/ Fiat dealer through the Parts Department for no charge, but you'll need to present proof of ownership at the counter (in person). This would be an excellent opportunity to add keys to the car because you can just serial-program up to 8 keys while the tool is connected. If nothing else, you might consider having a junk key cut that will just open the doors if nothing else. Key blanks are available over the Internet for considerably less than the factory ones cost, but they're notoriously finicky and often just plain refuse to program.
That's about all I have to say about that. So sorry that you're made to suffer, please write back if there's anything I can answer.