apparently ac11 doesn't get skip battle button.
Quoting the news.
The game will have 3 modes:
Full RPG experience
This would be considered the most complete way to play, you will have maps to travel, secrets to find, figure out where to go and what to do, and of course, fight opponents and improve your skills. To sum it up, it's exploration and free roam in addition to the two modes below.
Only combat
In this mode, you will skip pretty much all the "traveling and exploration" but you will still have the battles with the opponents.
Visual novel only
This mode focus is to be a novel, it's solely based on the story and the choices you make, and doesn't require tactics or investigation from the player, all combats are auto wins.
Full RPG experience and Only combat will have a mode that allows you to skip the battles... Or not if you dare 
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