This is what's happening with the SX Mini SL:
The guy who responded to the video says, "tu te mette sur l'écran d'accueil standard comme si tu allais fumé, et tu clic deux fois vers le haut pour remettre la luminosité," which I understand to mean he's advising the fellow with the problem to hit the fire button when the flash screen (briefly) appears and then nudge the joystick upward and click twice. At least, I think that's what he's saying. I haven't tried his solution yet, since I don't feel like struggling with the thing right now. Tomorrow will be soon enough. But if anyone here recognizes the problem in the meantime and has a fix in English, I'd be grateful.
I only had that problem with the first battery install. The SL just has a 5 click speed sweet spot. Find it and you're gold.