Despite the popularity of plug-in devices and rechargeables, 9-volt batteries still power smoke alarms, clocks, and walkie-talkies among other devices. As a responsible citizen, you don't just throw the batteries in the trash when they're spent. You know they contain toxic metals that shouldn't end up in landfills. Instead, you keep your batteries in a container or a drawer until you have enough to take to a battery collection station.