What are the rules for charging?
Charging into battle is not one of the combat options covered in ArM5. Treat a charge as using the Exertion option (p. 173) to increase Attack. This can be done on foot or on horseback (mounted combat rules are on p. 174). There are no special rules for a mounted charge, so it’s unclear whether the horse would need to spend a Fatigue level. The rider certainly would, to get the Exertion bonus to attack.