The individual soldiers in the battalion would have their own health bars just like now. They would just be locked into battalions and move and act like in Battle for Middle Earth 1 and 2.
To test this particular map with all civs, I'd need to make some more "generic" skirmisher replacers, based on battlefield role instead of class (heavy infantry, light infantry, etc.). Not impossible, but some work.
Yeah, I can do that now!