Hi posted on Facebook but not had a conclusive answer.
Failed Charges.. PAGE 19 para 4.3.
So according to this a charge will move it's maximum move even if target evades, unless evaders evade over Difficult Terrain or friendly chargers get in the way. Example. So if cav charge horse archers in open. HA evade. Cav move full distance towards them. They can't stop at half move. ????