The charge spell imbues the caster's dagger with magical energy which is discharged upon a successful attack. The discharge of energy will deal additional damage to the recipient at a ratio related to the Hero's magic skill.
The animation should be a form of glow or energy traveling from the caster to the dagger. There should also be a discharge animation upon a successful attack.
When cast outside of combat, the dagger should remain charged until sunrise or sunset, whichever comes first.