Why is it that, even though my battle size is set to 150, I only get a max of 50ish troops on at once? And, to answer the obvious, my army size is around 120.
Enemies sometimes get more but still never get near the limit.
a battle size of 150 means 150 total not per side. so combine the enemies units and yours and it will = 150.
If you want bigger than that you can get this mod: http://www.mbrepository.com/file.php?id=1761
but there is a stability risk for going higher than your system can handle.
The important factors are....
Leadership
Renown
Charisma
Leadership also affects Morale which you need to be high to keep your troops happy. Have lots of differnet types of foods in your inventory to improve morale also.