Vermilion City’s Pokemon Gym specializes in electric-type Pokemon. Electric-type Pokemon are only weak to ground-type attacks. Moreover, their electric attacks won’t be able to touch ground-type Pokemon. If you don’t have any ground-type Pokemon, you can find some in Diglett Cave to the east of Vermilion City.
To get to the gym leader, you’ll have to find two switches in the trash cans around the gym. They’ll change randomly, so it’s partially based on luck. Once you find one, look in a trash can nearby to find the second. If you can’t find the second directly after finding the first, the first lock will reset. There are three Pokemon Trainers in this gym before the leader.
Lt. Surge is the electric-type gym leader in Vermilion City. Interestingly enough, the game developers took it easy on players with this team. If you can defeat the Trainers before Lt. Surge, you should be able to defeat Lt. Surge. Voltorb and Pikachu are easy enough to deal with, but Raichu can be strong. His main weakness is the fact that he only has electric-type attacks. If you use any ground-type Pokemon, it cannot be taken out by Raichu!
The Thunder Badge will increase your Pokemon’s speed and allow you to use the HM Fly outside of battle. You will also receive TM24 Thunderbolt for winning.