'02 Dakota keyless entry

[66FBCharger]

The original battery in my '02 Dakota died Friday. It started fine when leaving work, but was dead (clicking the starter when attempting to start) when trying to leave a store. I went to NAPA and got a new battery and installed it. The truck fired right up.
When leaving working, my keyless entry worked fine and unlocked the doors. After installing the battery the key fob no longer worked. I changed the key fob batteries and the fob still doesn't work. What could be the issue? Could the battery dying cause a module to forget some kind of code needed to recognize the key fob? The owners manual talked about programming the key fob. Do I need to do that? I can't find my extra key fob so I can't check that to determine if the original key fob is at fault or not.
Does anyone know how expensive it is to get an extra key fob?
Thanks!

[LaOtto70Charger]

I am not sure on how hard it is to reprogram key fobs, but I can tell you that when my original battery died it did not affect my key fob working.  Recently also left it part way on with the key out and I had no issues after recharging the battery.  Are the locks working normally from the switches in the door?  Still lock automatically at 15 mph?

[66FBCharger]

I am not sure on how hard it is to reprogram key fobs, but I can tell you that when my original battery died it did not affect my key fob working.  Recently also left it part way on with the key out and I had no issues after recharging the battery.  Are the locks working normally from the switches in the door?  Still lock automatically at 15 mph?

Yes. the locks are working properly from the switch and lock automatically at 15 mph.