Introduction: Emergency Micro Powerbank

Hello Everybody!
I'm Manuel and in today's project I want to show you how to make a tiny emergency powerbank that could potentially save your life!

We all know that our smartphone's battery is always out of juice when we really needed it, for example to make an important call or, in the worst case, to call for help or rescue.

So, in order to overcame this eternal problem I designed and built a powerbank that you could attach to your keys or throw in a pocket and it will be always ready to charge a little bit of your smartphone battery.

Let's do it!

Step 1: Materials

For this project you will need:

  • A single cell Lipo battery (mine is a 300mAh 3.7V 1s)
  • a resistor (the right value is explained during the built process)
  • Usb step up circuit (5V 600mAh)
  • Single cell lipo charger (TP4056 board with protection)
  • a little switch
  • An little enclosure/container (I used a mints tin box)
  • hot glue gun with hot glue sticks or double-sided tape
  • soldering iron + solder
  • Dremel tool
  • heat-shrink tubes

!IMPORTANT! : My idea is to give to this little powerbank a sort of apocalyptic and emergency look. So, during the project I'll use some tools and materials to accomplish this goal. I want to underline that this is something unnecessary for the working of the device and you could simply use a different type of container (metal or plastic) without any problems. I just want to share my way of doing it but it's not the only or the best way!

Also talking about the battery, as I mentioned before I'll use a 300mAh single cell lipo. I know that it has a very little capacity compared for example to a phone battery (3000-4000mAh) but I have only this one at home and because I want this power bank to be as compact and lightweight as possible. You can freely choose a bigger capacity battery paying attention that it fits in the container you chose.

Step 2: Prepare the Tin Box

As I said in the introduction, I wanted to give to this micro power bank a particular look. I imagined it as a piece of a post-apocalyptic survival kit.

If you have another type of container (like plastic) or simply you don't want to give it this style, please skip this step!

Firstly I removed the paint of the tin in precise points (to simulate the wear) with the help of my Dremel tool. Then I refined the previus work using 200 and after a 600 grade sandpaper to give it a better finish.

After that I placed the tin into a container full of water to induce the formation of rust on the surface of the tin.

After a day, a thin layer of rust was formed so I applaied a cover of high-resistent transparent paint to protect the tin box from extra rust and wear!

I really like the final result so let's pass to the electric part of the project!

Step 3: Let's Wire Things Up!

Before putting all the components into the tin, I just want to temporarily solder all the electronic parts together just to make sure everything works and the battery isn't overheathing, inflating or, in the worst case exploding!

- First of all let's focus on the TP4056, the charging module. It's made to charge a huge variety of single cell lipo and the output current can reach 1A. However, as you may now, every lipo battery shouldn't be charge with a current that exceed 1C, one time his capacity. For example, the best way to charge a 2000mAh lipo is applaing a maximum current of 2A. In my case I have a 300mAh lipo, so the charging current has to be 0.3A, not the 1A of the stock TP4056 circuit.

Luckily, this board has the possibility to reduce the output current by replacing a particular resistor on the board. I found a tab on Google that show all the different current related to different resistor value. I replace the original 1.22KOhm resistor with a 10K resistor so the OUT current is 130mAh. The process is very simple but you need to be really precise (a small tip soldering iron helps a lot!). There are several tutorial of this on google, youtube and also here on Instructables. If you have a bigger capacity lipo, choose the right resistor value on the tab.

Now we are ready to start soldering things together!

First I cut off the little connector from the tiny lipo and then I exposed the two little wires.

I soldered the positive of the battery (red wire) to the B+ terminal and the negative wire (black wire) to the B- terminal of the charging circuit.

Let's proceed by soldering a wire between the OUT- terminal of the charging circuit with the IN- of the step up. The last wire goes from the OUT+ terminal to the IN+. Notice that I put a little switch just for testing and checking if everything works.


After doing all the connections, we are ready to test it! First I charged up the tiny battery by plugging a micro usb cable! After approx. 1 hour the light became green so the battery was full!

Then, using the step-up circuit I tried to charge my phone, paying attention that nothing was overheating or burning. Surprisingly this little monster was able to charge a 8% of my phone battery.

So, let's put everything into the little box!

Step 4: Circuitry Inside the Box

At this point, we are ready to put all the components inside the tin box and replace the temporarily connections with strong and durable ones.

First of all, I figured out the best way to arrange all the parts inside. As you can see from some photos, the back of the thin isn't a completely flat surface and this is a problem when it comes to fix the components to the tin. Moreover it's made of metal that could potentially cause a short circuit. So first I cut a piece of black plastic of the same size and shape of the interior of the box and then I glued it in place with some hot glue. All the circuitry is attached to this plastic plate and held in place firmily by some strips of double sided tape. Using the Dremel I make some holes in precise points of the tin, one for the Usb output, one for the micro Usb of the charger and the last one for the little switch. This last component is simply soldered to the box (you can simply use some epoxy glue). It is important because it prevents the battery from discharging over time.

Now that everything is in place we have to charge the battery and then carry the little beast always with us!

Step 5: Finish!

Let's make some final considerations:

  1. This device is intended for an emergency use. It cannot fully charge your smartphone or other devices battery. It has a small battery in order to reduce its size and weight.
  2. You need a small USB cable in order to connect the powerbank to your phone (otherwise the powerbank is useless). I-m already planning to make or buy a short cable that can be fitted inside the box so it's always ready-to-use.
  3. I know that on the market there is a huge variety of powerbank of different size, capacity, weight and price but in my opinion even the smaller ones are quite heavy (they have a 18650 lithium battery inside) and tends to discharge easily so they are completely dead when you really need them.

I know that the one I built can charge a small amount of a phone battery but trust me, in some occasions I would have paid for having such a powerbank that can charge only an 8% of the battery.

I'm planing to improve the beast by adding some LEDs so it will become also an emergency flashlight!

I had so much fun building it and writing this instructables so I hope you enjoyed the project! if you have any doubts or questions please leave a comment! I really appreciate it.

See you soon with another DIY project!