Make 9-Volt Batteries Last as Long as Possible

Here’s how to use every last drop of charge from 9-volt smoke detector batteries.

9-Volt Flashlight

Use every drop of energy from a 9-volt battery by adding it to an LED Blocklite.

Photo by Derek Purdy

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I was always stumped about what to do with partially depleted, 9-volt smoke detector batteries. They’re usually drained enough to cause the smoke alarm to chirp (typically at 2 a.m.), but they still have some juice left, so I hate to just recycle them. I looked around for another device to use the batteries in, such as a transistor radio, but few items use 9-volt batteries anymore.

Recently, however, I found a little LED Blocklite flashlight that does use a 9-volt battery. For about $5, you can turn your old battery into a compact — and surprisingly bright — flashlight. Now my little light goes with me on evening walks, and it lives on my nightstand. I plan to get several more!

Derek Purdy
Sunnyvale, California