Let me start by saying that the file structure for Mario Kart 8 on the Wii U is kinda dumb. See, the battle courses in MK8 Wii U share a folder with their proper race course counterpart, MK8 Deluxe is set up differently. What this means is, that while we can modify battle courses in MK8 on Wii U, it will lead to the normal race Course no longer being usable for actual races.
So, my solution was to have a mod pack (well 2 mod packs really, I'll explain in a moment) dedicated strictly to Battle Mode on Wii U. This mod pack implements all the Deluxe battle maps, but this modpack really shouldn't be used for racing unless you know which 8 courses to avoid for races during your play session. What's great about this though, is that we get proper Mario Kart 64 battle rules in the Deluxe battle courses, something that even Deluxe doesn't quite offer: 3 health, and no respawn upon death, when playing with others, when you die you're a ghost (kinda like the bomb in Mario Kart 64) that can still damage others.
Anyway, check out my video here, the download link is in the video's description on youtube:
I created a suite of 6 mod packs for Mario Kart 8. 2 of them are Mario Kart 8 Battle, and Mario Kart 8 Battle Lite, they're showcased toward the end of the video. They both have the same Deluxe battle courses, but they have different racers and karts. Lite is all the original racers and karts, Battle has a bunch of new racers and karts replacing others as showcased in the video. Please note the download is large because it's all 6 modpacks, I did not upload them separately, so I'm sorry that it's a larger download. Hope this is in line with what you're looking for.