9V batteries are not the most common battery form factor in photography, yet they are still being used in some remote triggers and RC related gadgets (like remote microphones). And of course for igniting steel wool.
While we generally recommend recycling batteries, you should watch that movie before recycling a single 9 volts battery.It shares the story of Dave from Kids and Character. Dave house went of fire when he placed an exposed 9V battery in a recycling bag and the contacts shorted. This led to the battery waring up and eventually catching fire which burnt down the house.
Dave’s tip is simple: gaffer tape the battery terminals before sending it on its last way. It will keep the contacts from shorting.
Thanks for the heads up Robert.