Get Power from ‘Dead’ Batteries by Building a ‘Watt Wringer’

Reader Contribution by Bob Post
article image

Batteries have a limited working life. Even the best batteries won’t last forever. When your electronics say “low batt” it means just that: The batteries are low but not dead. They can still have useful energy in them.

The energy that remains in seemingly dead batteries can be used in this simple night light project that you can build at home in about one hour. Your new night light will shine for months and is reusable for years, powered by “dead” batteries.

How to Wring All the Energy from a ‘Dead’ Battery

New, single-use batteries start with 1.5 volts. However, modern electronics generally stop working when the voltage in a battery reaches 1.2 volts. To be clear, we’re not talking about bringing a “dead” battery back to life but simply harvesting the rest of the energy that remains inside. Until now, remaining energy was wasted when a battery was recycled or sent to a landfill. That wastes energy and money.

This isn’t a new concept. It’s based on the Joule Thief circuit that has been around for decades. I don’t like the term Joule Thief so I renamed it a “Watt Winger.” The teaching version of the Joule Thief circuit uses transistors and a homemade transformer. Fortunately, a solar-powered garden light has compressed all of this onto a single electronic circuit board—much better for use with the Watt Wringer. Repurposing the circuit board from a garden solar light into an attractive and efficient nightlight is easy.

Don’t worry! There is no engineering involved and there is no chance you will be shocked by the electricity

Watt Wringer Materials List

Supplies you will need:
• Solar-powered garden light – new or used
• Wire cutters – or substitute toe nail cutters
• Screw driver
• Soldering iron
• Solder
• Battery holder – lots of options for these
• Switch (optional)
• Enclosure (optional)
• Hot melt glue (optional)
• Heat shrink tubing or electrical tape (optional)

Step 1: Find a Donor Solar-Powered Garden Light

Those little solar-powered garden lights seem to be everywhere.

Inside a solar-powered garden light is a clever electronic circuit board that is still working long after the garden light stops working. New solar-powered garden lights are not too expensive but used or damaged lights are less expensive, sometimes free. Maybe a used solar panel is cloudy or someone ran over the light with the tractor. Hey, it happens!

Note: A cloudy solar panel will have reduced performance.

Step 2: Disassemble the Top of the Solar-Powered Garden Light

Let’s start by opening the solar light and following the wires.  The battery is easy to see.  

This solar light uses a battery that is shorter than a standard AA battery. Other parts are not so easy to identify in the photograph so here’s a simple diagram that may help.

The circuit board is connected to the battery with two wires and to the solar panel with two more wires.

Step 3: Identify the Type of Solar-Powered Garden Light You Have

Some older solar-powered garden lights have a solar panel PLUS a photo diode (wait, I thought you said there wouldn’t be any engineering?). A photo diode is just a light sensor. These light sensors are small and round with a squiggly looking pattern. Light sensors turn lights on and off automatically at dusk and dawn.

For the simple night light we’re building, we will be using solar-powered garden lights without light sensors. Besides, they’re just not that common anymore.

Step 4: Inspection and Testing

Remove the battery and follow the wires from the battery to the circuit board. If the circuit board has damage from a leaky battery or physical damage (remember the tractor?) it’s time to find another solar-powered garden light. Circuit boards aren’t worth fixing.

Even a circuit board that looks OK, it might not work. There’s also a chance the LED light could be burned out.  To see if the circuit board and LED are still working, install a battery you know is still good.  When you cover the solar panel on top of the garden light, the LED should illuminate.

Step 5: Harvesting What You Need For the Project

If you have a working circuit board and LED light, you have found your donor parts. Remove the battery again and cut the wires between the solar panel and the circuit board. There are small wire cutters for small projects like this but nail clippers work pretty well, too.

Next, carefully remove the circuit board from the garden light housing. A hobby knife and some patience will remove the adhesive. Be careful not to damage the wires—or yourself!

Before you cut the wires to the battery holder, test the circuit board and light one more time just to be sure the circuit board was not damaged when removing it from the housing. With the battery installed and the solar panel disconnected, the LED will still illuminate if everything is OK. If the LED is still working, congratulate yourself. That was the hard part.

Step 6: Start Building Your Night Light – Choose a Battery Holder

Choose the battery holder you want to use. In this post, we’re focusing on AA and AAA batteries because they are the most common. Larger 1.5-volt batteries such as C or D size can be used, too.

The donor light in the photos has battery holder that was molded into the solar-powered garden light itself. This light is intended to be used with smaller, non-standard batteries so full sized batteries will fit. Some solar power night lights have full sized battery holders that can be reused.  If that’s the case for your project, carefully cut away any parts you don’t want. As an alternative, find a battery holder in another electronic device such as a damaged remote control or camera. Still another alternative, you can use battery holders from electronic supply stores like Radio Shack.

There are lots of options for battery holders.

Step 7: Choose an Enclosure

Speaking of options, there are also lots of ways to enclose your new nightlight. You could install it in a plastic jar or some other container. These clear, pointy containers in the pictures below are rejects from a plastic bottle making machine. Great for camping or backpacking because they are compact and waterproof.

You can also leave all the components completely exposed for a high tech look. There are also alternatives to build your nightlight inside something else like this metal lantern designed for tea lights.

This little battery holder below is designed for four AAA batteries and has a convenient switch built in. It has a compact stealthy appearance. Also good for camping or backpacking but is not water tight. It’s inconspicuous on a shelf.

In the photo above you can see the battery and circuit board inside. A small hole through the side of the battery holder is for the LED to shine through. The circuit board is held in place with hot melt glue.

Your enclosure might influence where you add a switch and how much wire you may need to add to reach the switch. Small enclosures won’t need any extra wire.

Step 8: Add a switch (Optional)

For this light, we’re going to add a switch to make it easy to turn the night light on and off. The switch is optional. Slide switches can be removed from small appliances or other electronics. Buying these new can be a little expensive. Right now prices are low at Radio Shack but there are also many other online electronics suppliers such as Mouser and DigiKey.

There are lots of slide switches to choose from. Any switch will work because voltage and amperage is very low in a Watt Wringer.

Slide switches have flanges that make mounting easy. The switch can be held in place with screws or hot melt glue.  Slide switches are a low cost solution. Toggle switches can be used too but they’re more expensive to buy new.

You could eliminate the switch and remove the battery when you want to turn off the light or just leave the light on all the time. Naturally the battery won’t last as long if the light is on all the time. Since our goal is to save energy so we’ll turn the light off when it’s not needed.

Install a switch in one of the wires between the battery and the circuit board. It doesn’t matter which wire but it’s conventional to install a switch at the positive side of the battery.

To make the connections at the switch, remove a short section of insulation at the end of the wire to expose the copper inside. Connect the wires to the switch. Electrical connections with small wires like this are usually made by soldering. Shrink tubing or electrical tape will protect the wires from accidental short circuits. A short circuit at the switch will keep the light on all the time.

Before you install your new nightlight into a housing, let’s check it again to make sure it lights up.  If there is a problem, it’s easier to fix it now than after everything is inside the enclosure.   Install the battery again and flip the switch back and forth.

Step 9: Enclose or Not to Enclose?

The last step is to put everything into the enclosure and mount the switch. The possibilities are as endless. You don’t need to put the Watt Wringer in an enclosure. It can just sit on a table and be a conversation starter.

For this example, I chose to replace an incandescent light bulb with a Watt Wringer. A deck prism is a piece of glass that ship builders placed through the top deck of a ship to allow light to enter the decks below.  I like the contrast of old school lighting with today’s electronics.

You’ve probably noticed that most of the light leaves an LED through the end away from the wires. Bend the wires so the LED points in the direction you want the light to go.  In this case, I bent the wires so that the light goes up, through the glass. The switch is easily mounted through a hole in the plastic base. Hot melt glue holds the switch in place.  If you’ve read this far, you’re probably handy enough to install a switch without any further instruction. But if you need some help, please feel free to leave a comment in the box below.

Step 10: Next Steps

Save your batteries! Other people also save their dead batteries and give them to me. Maybe people you know will save batteries for you. Better yet, show others how to find this blog post on MOTHER EARTH NEWS so they can make a Watt Wringer for themselves.

After a few weeks or months the light will start to flicker. When that happens, it’s time to replace the battery with a different “dead” battery. When the LED is flickering, the battery is really nearly dead at around 0.6 volts. Then you can recycle the battery knowing you got the most energy possible from it.

Congratulations! Your new nightlight will wring lots of Watts from your batteries.

If you have any questions about this blog, please leave them in the comments below. You could be helping other people who may have the same question. If you prefer, email me: My contact information is on my bio page. Thanks for following this blog post and be on the lookout for more of my DIY projects from MOTHER EARTH NEWS.

All MOTHER EARTH NEWS community bloggers have agreed to follow our Blogging Best Practices, and they are responsible for the accuracy of their posts. To learn more about the author of this post, click on the byline link at the top of the page.