Over the past week, I tried a bunch of pet battles addons. These are the ones I keep using. Basically they provide all the info you would ever need, and make the UI a bit better / more informative.

Pet Tracker – http://www.curse.com/addons/wow/pettracker
Pet Battle Master – http://www.curse.com/addons/wow/petbattlemaster
Petjournal Enhanced – http://www.curse.com/addons/wow/pet-journal-enhanced

You can see them in action in Episode 7 of Pet Battles over on Youtube !