On my raspberry pi 3 running Batocera, I was trying to connect my SteelSeries Stratus xl bluetooth controller.
In terminal when I run sdl2-jstest: INFO: The key you just pressed is not recognized by SDL. To help get this fixed, please report this to the SDL forums/mailing list <https://discourse.libsdl.org/> EVDEV KeyCode 304
Also several of the keys show this message: SDL_JOYBUTTONDOWN: joystick: 0 button: 2 state: 1 code:172 Error: Unhandled event type: 769 SDL_JOYBUTTONUP: joystick: 0 button: 2 state: 0 code:172