"Each spell can only be stored by one battery/capacitator. "
The damage will stay at a pretty low level since stacking multiple batteries has no use. As I said before, the damage potential of Fractal, Paralel Universe, Firebolt and Drain life are much higher.
This card also has the disadvantage to be a permanent (as opposed to the spells mentioned earlier) and it has to be around for a while to get full nuke effect. In my opinion this is what makes it balanced.
ah yes I see where I missed that part. Also you said you wanted it to stack but thought it'd be OP. Well how about if you made it 1 damage per counter and let it stack. Also changed it to
:Discharge: Unload all damage onto Target.
This way it could also target creatures.
Just another idea for it.
