It's a little annoying when you are in a battle, and someone joins, but goes afk right away. Even if it's a friend. I have two suggestions that would fix this small annoyance.
(1) An AFK status button (which would be convenitent in other aspects of the game as well) so that if you are AFK during the battle, it acts as if you weren't there. So this way, when the other players have picked their cards, it doesn't wait for the person who is AFK. This option could also potentially affect the amount of xp you earn from that battle.
(2) If a person fails to choose a card for three turns, they automatically get teleported home.
Seems the better choice would just be to have an AFK status, but something would be nice so that players don't have to sit and wait for the timer to run out for the entire battle if someone decides to go AFK. Thanks!
Be careful about the not choosing a card bit. Someone can easily miss a couple of turns from a client crash before making it back into the game. Missing a couple of turns and then being able to pick up the battle with the extra pips from those turns hurts some, but automatically fleeing whenever the client crashes would hurt a lot worse.