So you get overcharge ONLY from casting spells right? Why not add a clickable you can use without casting any spells (just have a very long cool down of course) just like Sniper's take aim active now. When you get overcharge at level 1 it is useless since you need to cast spells first, plus it would be really great with the level 25 talent that goes through BKB and especially if you get Aghanim's on Storm.