Right now they are way too similar to Sturgia in playstyle (tons of shield infantry, javelins, jav cav and one handed axes). They lack a clearly defined strength or weakness, basically doing everything at a mediocre level (it would be fine for them to be a "generalist" faction except that Vlandia, Aserai, and 3 different Empire factions are already generalists!) Their army composition could do a better job of matching their culture description and their Celtic inspiration. So changes are needed.
* Turn the Clan Warrior into a shock infantry troop from T2, this will make Battania have more shock infantry than any other faction, being accurate to their culture description. They have a small targe as backup, to help protect against arrows.
* Remove the Battanian Horseman for the previously mentioned reasons.
* Add a new shock infantry troop, the T5 Gallowglass, branching from the shield infantry line. To differentiate itself from the Veteran Falxman, it uses a two-handed axe, wears heavier armour, uses throwing axes, and has no targe. This will make Battania's culture description accurate and further increase their unique niche as a shock infantry faction.
* Change some of Battania's troops with large shields into troops with long pikes. This will make them more unique from Sturgia.
This would make them more unique in gameplay, and more representative of their Celtic inspiration. Leaving aside Braveheart's historical inaccuracy, this video clip sums up 1000 years of Celtic armies' general approach to battle: