If you disconnected the batttery, you also put the radio in a recode mode. if so, you will nedd to ennter the code for that particular radio using the number keys or buttons on th radio.
Also, to get the battery out you need to remove that rear seat cushion and on the il it is easier to:
1. Take buttons off of seat and head rest adjusters (they pull off).
2.Remove the two screws holding the plastic trim in place and remove the trim.
3..If your battery is dead, then disconnect the seatbelt electrical connector on outboard side of seat.
4. Remove the bolt (13MM I believe)that goes horizontally through the seat belt attachment rod.
5.Now, yank front of sest cushion up and then slide it out of the seat back cushion (two curved rods that slide up into the seat back).
6.Lift cushion and disconnect the under seat wiring connector and set seat aside(some of thesr cushiond have a push button on lower front of cushion that also acts as a release.
7. You now have access to your battery.
Reinstall is reverse of removal except, I would move the seat cushion all the way foreward and also move the front passenger seat all the way foreward (working room). Getting the seat cushion rods back and up into the seat back is a real PITA the first time, takes lots of patience and many bad words.