You’ll unlock your first set of Battalions after completing the quest “Leading the Charge”. However, the Battalion Guild facility will be unlocked on the month of Garland Moon (06), after completing the quest “Bolstering Forces” from Jeritza.
The guild is located in the Marketplace and can be accessed remotely from the activity selection or Battle Preparation screens. Here, you can manage the Battalions you can assign to each of your character. It’s imperative to give every character their own battalions since they’ll get Stat buffs and enables said characters to perform Gambits. Please refer to this guide’s individual sections regarding battalions and gambits.
In the Battalion Guild, you have three options: Hire, Dismiss, and Replenish.
Hire new battalion and assign them to a character. This is done whenever new battalions become available from the guild or when you get a new character. One thing you have to consider is the battalion type you’ll assign to a character. Pegasus Rider characters for example can only take in Pegasus Knights battalions. Try to assign battalions that somewhat match the assigned character’s class to maximize their effectiveness.
Another thing to consider for Battalions are their required Authority level. Rank E battalions can be assigned to almost anyone while Rank D or above will require the corresponding Authority levels.
When hiring a Battalion, you can review their descriptions, the boosts they provide, and their Gambit’s effect/Range.
Remove a battalion from your list. You don’t really need to use this feature since you’ll probably assign your Rank E battalions to your other characters, especially those with low Authority levels just to give them the necessary support and boosts.
This option will restore the endurance of all your battalions. Thankfully, the cost to replenish them are very cheap so don’t hesitate to use this option regularly, especially before going to battle.