After defeating the Elite Four and becoming the newest Kanto Region Pokemon Champion, you can battle all of the Gym Leaders in a rematch on a daily basis back in their given Pokemon Gyms. Each Gym Leader will have a team far different than the one you faced originally, usually being much stronger than before with additional Pokemon too. On top of this, you will earn Experience and Money every day you defeat them.
When is comes to Lt. Surge, the Vermilion City Gym Leader, his team has changed greatly. Instead on having nothing more than a Voltorb (Level 25), Magnemite (Level 25) and Raichu (Level 26) originally, he now has a team of five Pokemon with levels greater than fifty. To be exact, all of his Pokemon this time around will be at Level 56, with the exception of his Raichu that will be at Level 57. If you put this into perspective, you will quickly realize these are similar numbers to the Pokemon your Rival had during your Championship Match! In all, Lt. Surge will battle with Electrode, Jolteon, Electabuzz, Magneton and Raichu.
Just like your first match against him, Lt. Surge's Pokemon Team will have a major weakness against Ground Type Pokemon. Not only are all of Lt. Surge's Pokemon weak to Ground Type Attacks, but their Electric Type Attacks do no damage whatsoever to Ground Types. Honestly, a couple of Ground Type Pokemon is all it should take to defeat Lt. Surge, preferably at Level 55 or greater in order to match up well.