Worn AA Batteries Get a Second Life

The "Duck light" project earlier was a lot of fun, crafting an object to be lit with a little LED tea light. I liked the result so much I kept it lit around the clock, which led to the obvious next problem: battery life.

These lights came with a standard CR2032 lithium battery good for 2-3 days of continuous use. Replacement batteries can be found for less than a dollar, but that's almost as much as the cost of the entire light! I embarked on a project: find a better way to keep my lights glowing.

Online search found some basic details on CR2032. The full power voltage is 3 volts, conveniently a multiple of the ubiquitous AA battery's 1.5 volt. More interesting, however, is that the quoted minimum voltage is 2 volts. Most AA-powered devices would stop working well before an AA battery drops to 1 volt, which implies that a "spent" AA would still deliver sufficient power for the tea light LED.

With this research in hand, I proceeded to design and 3D-print a small battery tray as simply and inexpensively as possible. Normally an AA battery tray has metal springs to push against the negative end of the battery. My project takes advantage of the fact the 3D printed plastic is flexible, and print a curved arch to provide this holding force.

I need something at each end of the tray to complete the circuit. One end is easy: I pulled the LED component out of the tea light base and used pliers to shape the wires into a Y shape to connect the battery terminals. At the other end, I used a piece of aluminum foil from the kitchen. Normally this is a bad idea because a thin foil of aluminum can't carry much current, but it should be fine given the extremely low power flow of the LED.

To make the base more presentable, add a cosmetic shell to cover the battery tray and provide support for whatever we want to keep lit, and voila! A small lighted base for any purpose.

I had a pair of AA batteries that had been in my Xbox One wireless controller. I received "battery level low" errors for about a week before the controller refused to turn on at all. Yet these batteries were still powerful enough to light up the LED and keep them lit for many days.

A cheery light powered by batteries that would have otherwise been thrown away. Success!