Typical analog wall clocks can run down to about 0.4 volts. The battery will rot sooner than that though… Also, many batteries get trashed because the device cannot use them fully and shuts down when they’re at about 1.4 V… an example is anything with 2×1.5V cells, no boost converter, and a white LED. It’s a waste to put fresh batteries in a typical ticking wall clock unless it’s hard to reach. In fact, using recently “depleted” batteries from devices that don’t run below 1.2 V will force you to replace them about bianually (clock size and battery type affect which meaning of the word) and avoid them getting too old and corroding.

You can recover graphite rods from carbon zinc or “heavy duty” batteries. Alkalines are trash though, and you shouldn’t keep then around because they have a tendency to burst.

Nice double entendre, despite the inert punchline!

They say it’s free of charge, but when I take them, they call me a joule thief!