Lithium ion (Li-ion) batteries can work wonders for portable Arduino projects.

Chances are, you probably have tons of them lying around that you're not making use of. You can salvage them from many rechargeable electronics such as cellphones, cameras, MP3 players, etc.

An annoyance I came across when using these batteries in my projects though, is when I have to transfer a Li-ion battery from one project to another - I usually have to open up an old project, desolder the battery, and solder it into the new project.

To solve this problem, we're building a modular power cube - a Li-ion battery cube that can be easily attached and detached from one project to another. It also comes with the charger and power switch!

Step 1: Watch the Video!

Check out this quick video, for a run-through all the steps below from start to finish.

Click here to watch on YouTube

Where to buy

5v Booster/charger board: http://amzn.to/2dg2DuB
Li-ion battery: http://amzn.to/2dEDps3
SPDT Slide switch: http://amzn.to/2dB10XJ
RGB LEDs: http://amzn.to/2d8jkf4
USB connectors: http://amzn.to/2dmCCYr

Soldering gear:

Weller WES51 Analog Soldering Station: http://amzn.to/2daTxR9
MG Chemicals Silver Solder: http://amzn.to/2daTFzZ
Helping hand: http://amzn.to/2dsKAjC

Testing gear:

Multimeter: http://amzn.to/2cD90uc
Breadboard & Jumpers: http://amzn.to/2daUkS5

Step 2: Salvage the Battery

Safety warning: Li-ion batteries can be potentially hazardous and can present a fire hazard if damaged, defective or improperly used. Do not expose them to excess heat. Do not puncture them (they are pressurized inside).

For our purposes, we're going to salvage a 3.7V (single cell) Li-ion battery. Pictured above are examples of where you can find these batteries.

Step 3: Boosting the Voltage

A single cell Li-ion battery outputs around 3.7V, which isn't going to work by itself if we want to power Arduinos (like the UNO) that require a 5V regulated input.

So I'll be using a 5V DC Booster/Charger module. You can have them for around $4 USD. It comes with a mini-USB input for charging, and a standard USB for output. The B terminals are where we connect our lithium battery. It also has three LEDs on-board to denote the status of the battery (red - charging, green - charged, blue - load).

We're going to make a couple of modifications to this board to suit our needs. First we'll swap the output plug from USB female to USB male, and add a slide switch so that we can turn the host device ON and OFF. Then we're going to solder in a few LEDs into the external LED slots so that we can have LEDs on the case of the battery.

Step 4: Swap the Booster Output Port

Let's start by removing the USB female port from the booster and replacing it with a USB male port, so that we can plug our power cube into a host device.

We can salvage a USB male connector from a USB extension cable.

Solder in the male connector to the output port of the booster board, using a short ribbon cable.

Tip: don't solder the positive wire just yet (our power switch needs to be attached)!

Step 5: Attach the Battery and Power Switch

Here's the battery I chose, it's a 1800mAh (this is the capacity of the battery - the higher, the longer the battery will last) single cell, and I salvaged this one from a PSP battery expansion pack that I never used.

We'll solder the positive (+) terminal (or red wire, in this case) of the battery to the B+ terminal of the booster, and the negative (-) battery terminal to the B- terminal of the booster. When in doubt, check the polarity of the battery with a multimeter first!

I've also soldered a SPST slide switch to positive wire of the output port. This will act as our power switch and disconnect/reconnect power to the host device.

Step 6: Attach External LEDs

Next, we'll check which LED is which color, and a quick way to do that is to put our multimeter in continuity reading, and probe the two ends of the LED to light it up.

After we figure out which color is which, we'll take an RGB LED strip, and wire that up to the corresponding external LED slots.

At this point, we'll want to give our battery a test charge and make sure all our components are working as intended before we go ahead and build an enclosure.

Step 7: Make a Plastic Cutting Tool

There's many ways to go about building an enclosure - 3D printing, and laser cutting being some common options lately. But, we're going to be resourceful and build the enclosure out of recycled CD jewel cases.

We'll need to create a heated blade tool to cut CD cases with.

Take a leftover piece of blade from a retractable knife and mount it to a soldering iron by fitting the piece between the screw of the iron.

Tighten the screw so that the blade cannot move. Remove the solder tip.

Step 8: Cut Out Enclosure Panels

Using our heated blade tool and a straight metal edge, we'll cut out panels to fit our components.

Make shallow cuts, and snap off the pieces with pliers. This will create cleaner cuts rather than letting our heated blade tool melt through the plastic.

After we have our pieces cut, use sand paper to smooth the edges.

Step 9: Cut Holes for Ports and LEDs

Using our heated blade tool, we'll also cut out holes for the USB ports and power switch.

Using a drill, we'll drill holes to expose the LEDs.

Step 10: Glue Components Together

Use a generous amount of hot glue to firmly attach the USB output port through the hole of the top panel.

Use super glue to attach the rest of the enclosure panels together.

Step 11: Tape Up the Edges

To make our battery cube a little more aesthetically pleasing, I chose to seal up the edges with black electrical tape. This step is optional though, of course.

Step 12: Give It a Test!

We're done! Give it a test and try to power up any USB powered device.

In the picture above, I have my power cube charging a Blackberry while the power cube itself is being charged. The blue LED indicates that the battery is under load, and the red LED indicates that battery charge is in progress.

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That's all I have for you today!

If you liked this Instructable, then perhaps you'll like some of my other projects!

You can check them out over at my YouTube channel.

Next week, we'll be building a portable Arduino device that is powered by this power cube, and also makes use of the Bluetooth HID module from our last Instructable. So check back next week!

I'll see you then!