If you are looking for the original 1991 game or the Rare-developed classics, they are officially available on PC through the collection (via Xbox app/Game Pass) or specific retro bundles.
When searching for "Battletoads download PC game full version," be cautious of third-party "repack" sites or "free" executable (.exe) files. battletoads-download-pc-game-full-version
This is the most stable official way to play the original Battletoads and Battletoads Arcade on a modern PC. If you are looking for the original 1991