To get this achievement you must kill 25 enemies (skags, bandits ect) with weapons that have an electrical element.
These weapons have a blue lighting sign in the inventory menu.
Blue numbers will come off enemies if they are impacted by electrical damage. Electrical damage is like other elemental damage in the game in this is causes damage over time. The enemy does not have to die as a result of the elemental damage however.
You can check your electrical kill count in the challenge menu, go to the quest screen and press Y.
You can also use barrels for this achievement. Electrical barrels are blue.