It is about the cavalry charge :

had some similar problems but now i do it "my way".

i group 3 cav units on two lines and tight. then order the formation to move just behind the enemy lines. when close enough i give them "run" . and they do !!! smashing any unit to pieces ( if u dont believe me try it )
when in the back of enemy lines i order then now in the opposite direction ; same : they run again though the lines - battle over !

and that without using "charge"