Well I have a pet that is completely full and Very Happy, but it still says that none of my pets are elligible for battle.

Is there something else I need to do for them or what?

The second post here has a list of all the things that can stop your pet from battling. :) I hope you find the solution there!

This thread 'An Introduction to the Battle Coliseum' Will answer all your questions.

[edit] beaten by , linked to the same thread too. :)

Thank you both so much.