I know this question has been asked and answered many times but it seems that the answers have been creating just as many arguments.
When you acquire all 6 spell books combat becomes an Unlimited action and therefore NOT a Normal action and the player MUST perform a Normal or Unique action each turn. So to perform a combat the player must also perform a Normal or Unique action and of course must have enough power for both.
Or some people interpret this as the Combat action performs both duties as a Normal Action and Unlimited action.
When you have 6 spellbooks, Combat can EITHER be a normal or Unlimited Action.
Having 6 spellbooks does not lessen your options, it only increases them.
I'm pretty sure even the original (less well written) rulebook said that you can still JUST do Battle when you have 6. But, if not, the answer is yes.
You can ALSO do the following, if you have 6 spellbooks:
Battle as an Action.
THEN decide if you want to do another Action as you "normal" Action.
In other words, you don't have to predetermine if your Battle is normal or unlimited, if its the first thing you do.