$10 USB Battery Charger

•Intro

Every now and so often we need to carry some extra juice to charge up our phones. Like on campouts, for example! In our house, we have an 16,000 mAh iSound unit which has served us well. But, it's one heavy brick, and at $80, still pretty expensive. I wanted something smaller and lighter, good enough for a few charges. So, here is what you can build along those lines for a fraction of the cost..

Get the Parts

• Batteries: 2 x 18650s, which will provide anywhere from 4000mAh to 6800mAh
• Charging Circuit Board (USB): A 3-5v to 5v 1.5a phone charger CB. Any type of basic voltage boost circuit (to ~5v) should do. I got mine from Fasttech.com.
• Project Box: Anything with enough space for the above. Again, I went with Fasttech.com but feel free to experiment.
• Other: 1x "clicky switch" with tail, 24 gauge wire, glue (CA or hot glue)
• Optional: LED and resistors for On/Off monitor

Position the Parts

The first step is to arrange the major components where they will be going into the case, to make sure that everything will fit. For this, I de-soldered the USB port from the circuit board and re-attached it with wires. Then I hot-glued the port to stick out of out the front of the box.

Main Soldering

Next, I ran a wire to connect the 'ground' to the negative input of the charging circuit. You can leave this loose or glue it in place in a corner.

Then, solder one end of the clicky push-button switch to the positive input.

Finally, we need to bridge the two positive battery contacts. I just tinned a large length of wire and soldered it to both contact pads.

On/Off Switch

Now we're ready for final assembly. Solder the other end of the switch to the bridged positive connections. This will complete the circuit when the button is activated.

Then, position and glue the button where you can access it when the box is closed. Some cases, such as the one I used, have external controls so I positioned my switch to align with the external button.

Test & Finish

Now put in one cell and press the button. If your circuit board has an LED and your battery has any charge, it should light up this point. If all is well, plug in your phone and see if you get 5v output.

You are done! You now have a battery charger for your USB-powered gadgets.

Optional Add-Ons

LED Charging Indicator

Just add a 3mm LED with a 1k resistor across the positive and negative inputs of the charging circuit and put in in the provided LED opening, or just drill one out yourself.

TP4056 Add-On

You can also add a TP4056 circuit to charge the batteries while they are inside the case, meaning that once you have put the charger together you will never have to take it apart to charge it. This only works with 1-2 cell chargers, however, you can find these circuits for very cheap on eBay. This way, you can charge your batteries through a mini or micro USB Port like any commercial charger!