Emergency USB Power Source (3D Printed)




About: Making and sharing are my two biggest passions! In total I've published hundreds of tutorials about everything from microcontrollers to knitting. I'm a New York City motorcyclist and unrepentant dog mom. My ...

This project makes use of a 12V battery, like you would use for a vehicle, for charging USB devices in case of a power outage or camping trip. It's as simple as affixing a USB car charger to the battery. After Hurricane Sandy, I was without power and used an inverter/battery setup at home, but it was huge and heavy. This project revisits the concept with a smaller battery (meant for motorcycles/ATVs) and DC-only charging.

I've also created an optional 3D printed battery topper to cover the battery contacts and hold the USB ports. The design is available on Tinkercad so that you may modify it to fit your specific battery and USB charger.

The compact design makes it easier to transport and store. There are many situations where this device could be useful:

  • power outage
  • camping
  • off-grid living


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Step 1: Wire It Up

First I connected the USB charger to the battery to be sure it works, and take some measurements. The red wire connects to the positive terminal, and the black wire connects to the negative terminal. My charger also has a fuse. The USB charger can be used like this without the need for any 3D printed parts. It can be installed in a motorcycle dashboard or tucked away with your other emergency supplies.

The 8Ah battery at 12V gives me 96 Watt hours. Divided by my phones 11.2 Watt hours and factoring in a 90% efficiency of the USB charger, I can get about seven and a half full phone charges from this battery, or half that if I want to still use it to start a vehicle.


(8Ah * 12V) battery / (11.2Wh phone / .9 charger efficiency) = 7.7 charges to depletion

Step 2: Measure and Model

Use a ruler and/or calipers to measure your battery and USB charger and adjust the Tinkercad model to fit its dimensions with some tolerance (about half a millimeter of extra space should do), if needed. Definitely double check the measurements of your components before printing—I used an old battery that I can't find online and so yours is bound to be a little different.

My battery dimensions: 151.33mm wide x 84.40mm deep x 106.00mm tall

My USB charger dimensions:

  • 27.23mm diameter of threaded stem
  • 37.36mm nut outer diameter

Step 3: 3D Printing

After downloading the STL file from tinkercad, I used Cura software to prepare the model for printing. I flipped it upside down so it will print its flat surface first. Here are my print settings:

Step 4: Use It!

Unplug the USB charger and install it into the hole on the 3D printed topper using its included nut. Wire up the circuit (red to + and black to -) and set the topper on battery. Tidy up the wires by tucking them up into the empty space remaining in the front of the topper.

Turn on the USB ports with the included switch before using, and turn off when not in use.

Thanks for following along! If you make your own version, I'd love to see it in the I Made It section below!

If you like this project, you may be interested in some of my others:

To keep up with what I'm working on, follow me on YouTube, Instagram, Twitter, and Pinterest.

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    14 Discussions

    bekathwiaPerfect DIY

    Answer 4 days ago

    Grabbed the embed code from the public page (has to be public), inserted it into editor HTML view.


    5 days ago

    Nicely done and a great start. A couple of recommendations moving forward:

    1. As some folks mentioned, starter batteries are a poor choice. That said, in an emergency you use what you have. Those 7Ah AGM batteries used in UPS's, emergency lighting, kids ride on toys, etc would be my choice. They're everywhere.

    2. Incorporating a small AC/DC charger in the case would help a lot. My luck, I would find myself at a plug with a battery that needs charging with no ability to do so.

    3. To cut down on the weight while raising durability and capacity, perhaps we can use 18650 lithium cells. These have their own challenges, but the energy density is quite high.

    4. Used lithium cells (18650s) may be harvested from older laptops, power tools, wrecked Teslas, or other e-waste. While this version requires skill in testing and dealing with lithium cells, it might significantly cut the cost of the project.

    2 replies

    Reply 4 days ago

    Yeah this is the battery I have, so that was the starting point. Many ways to prep for a power outage, mine is to keep this thing on a trickle charger in case I need to use it like this or to jump a dead motorcycle (since there's no power where I store them). Thanks for your input!


    Reply 4 days ago

    Kinda figured that was the case. That is where all good projects start and is one of the foundations of Open Source; scratching that itch. Thanks for sharing! If you want to see what you can accomplish with the lithium calls, Jehu Garcia has some great info and sources.


    10 days ago

    Thi is a really good idea! Also good work on your enclosure design, lookin' sharp!

    1 reply

    5 days ago

    Minor issue. Lead Acid batteries (Even Deep Cycle Marine batteries) do not like to be discharged below 20%. Doing so causes loss of life/capacity due to sulfation. Great idea, though, love the 3D printed panel.
    I have mine in an ammo can with a cheap (Harbor Freight) charge controller, to prevent overcharging & over discharging. I hook mine up to a cheap wall wart or solar panels for charging, and use it for mostly ham radio and raspberry pis.

    1 reply

    6 days ago

    Please don't use starter batteries for this kinds of loads, you can safely discharge 30-50% of it's capacity, everything more that that will eat up electrodes and you will damage the battery. Instead, get deep cycle lead acid or lithium batteries. Other than that, great project, maybe it would be useful to also add 12V socket so you can hook up other things like 12V LED bulbs.

    2 replies

    Reply 4 days ago

    This is a $20.00 battery for small needs like charging phones for a few days.
    I would consider it semi-disposable compared to the $50 + for a deep cycle of 8 AH.
    If you planned on using it on a daily basis; deep cycle.


    Reply 4 days ago

    Where did you look at prices? Deep cycle batteries are really cheap, smaller ones are usually same price as starter batteries.This one is 24$ for 9Ah battery.
    Building your own using lithium cells might even be better if you can find good deal, i made 3S3P pack with 9Ah capacity for about 10$.
    I wrote this comment since she said that her battery gives her 96Wh of usable capacity, that is nowhere close to what you would usually get out of one without damaging it, also lead acid batteries discharge itself quite a lot so if you have bike that is sitting in a garage for some time or battery sitting on a shelf, it might be dead by the time you have to use it.


    5 days ago

    very clever very well done.