Add a node (or branch of nodes) that reduces Surge skill recovery time by N% of the affected monster (increases with the number of monsters).
Also, increases mana cost by N for each monster.
(I admit that for the balance need to add some more limiters or penalties.)
The purpose of the change is to give a stable skill for damage with lightning damage. At the same time, do not change the total damage of Surge on a single target.
I know I will be given the example of Flame Reave with the lightning conversion. But first, the skill itself has specific mechanics.
Secondly, I think it is wrong when the same skill is used in different builds, it hurts the diversity.
P S S
As an alternative suggestion, you can make an item, an amulet or a ring that will remove Surge’s cooldown, in exchange for any penalties.
Like the ring for Flame Reave.