Those little solar garden lights have become pretty ubiquitous in the past few years. They don't last forever though because the rechargeable batteries in them eventually don't last through the night after a day's charging and they ultimately get tossed into the trash. This instructable will show you how to turn those old solar cells into a solar batter which can be used to energize any USB-powered device using some wire, some recycled batteries, some electrical tape, a case of some kind and a couple of chips which will cost you around a Dollar/Euro each.

Please Vote/Favorite/Share/Make this Instructable, see more of my projects at http://justintylertate.weebly.com/ and continue on to the next step...

Step 1: TOOLS/MATERIALS

TOOLS:

Soldering iron and solder
Wire cutters
Hot-glue gun and hot-glue sticks
Scissors or knife

MATERIALS:

3-6x Flat Top Li-ion Batteries Bulk 2500mAh (*can be recovered from taking apart a laptop battery)
3x 1.5v Solar Cells (**can be salvaged from solar lawn lights)
1x TP4056 5v charging circuit ($0.27)
1x DC Boost Module step up Converter 3V 3.7V to 5V circuit ($0.80)
Some wire
Heat-shrink insulation
A project box or other case
Epoxy

I suggest you read the entire instructable before beginning so that you understand how to complete the project.

Step 2: CONNECT YOUR BATTERIES

Tape your batteries together in groups which will fit nicely into your project case. For example, my project case was quite long and narrow so I taped my batteries together in groups of two.
Solder wires to connect the ends of your batteries. It is really important that all of your batteries are wired in parallel (meaning that all of the positive ends are touching connected to each other and all of the negative ends are connected to each other).
Once they are all wired in parallel, tape your batteries together so that they are secured and the risk of shorting the circuit is severely diminished.
Now you should have a battery bank that can be charged and discharged.

*It is really important that you don't accidentally wire your batteries in sequence or make a short circuit anywhere.

**Originally when I was making this instructable, I thought to use 6 Li-Ion batteries, wired in parallel, for storing power however 6 batteries would not fit in my project case so I removed 2 of them.

Step 3: SOLAR CELLS

Solder wires to each of your solar cells, connecting them so that they are wired in-sequence.
Secure your solar panels to your project case.
Now you have a solar cell which can produce 4.5v on a sunny day to charge your batteries.

*To attach my solar cells to my project case, I hot glued the seams and epoxied a piece of nylon strap to the back side of them after doing the wiring. This allowed me to sew the solar cells to my project case. Because most project cases will be different, I suggest that you attach your solar cells to the case in the way which provides them the most protection as well as giving them support and allowing for a good angle to catch the solar radiation.

Step 4: CIRCUIT

Now is the time to assemble all of your components; the battery bank, the two circuits and the solar cells.

Following the schematic, you will need to:

Connect the wire coming from the positive end of the sequence of solar cells to the "In+" hole of the TP4056 5v charging circuit.
Connect the wire coming from the negative end of the sequence of solar cells to the "In-" hole of the TP4056 5v charging circuit.
Connect the wire coming from the positive end of the Li-Ion batteries to the "Bat+" hole of the TP4056 5v charging circuit.
Connect the wire coming from the positive end of the Li-Ion batteries to the "In+" hole of the DC Boost Module step up Converter 3.7V to 5V circuit (the red circuit board with the USB port).

*The following are also detailed in the next step:

Connect the center pin of the switch to the negative end of the batteries.
Connect the right pin of the switch to the "-BAT" hole on the TP4056 5v Battery Charger Circuit Board.
Connect the left pin of the switch to the "-IN" hole on the DC step up Converter 3V to 5V USB Charger.

For my project I was able to sew my solar cells to the project case because of the fabric I epoxied onto the back but Probably you will have a hard case so i suggest that you glue and mount all of your circuitry inside of your project case to the best of your abilities in a way that will keep everything safe. A step on installing the USB discharging circuit and the switch will follow in their own step.

Step 5: SWITCH

Connect the center pin of the switch to the negative end of the batteries.
Connect the right pin of the switch to the "-BAT" hole on the TP4056 5v Battery Charger Circuit Board.
Connect the left pin of the switch to the "-IN" hole on the DC step up Converter 3V to 5V USB Charger.

Flipping the switch will change your charger's function between discharging and charging your batteries.

Step 6: INSTALLING USB AND SWITCH

To finish your portable solar powered battery-bank, all you need to do is cut 2 small holes in your project box; one which will hold your switch and the other to hold the USB port.
Insert the switch into the holes and (hot)glue it into place and then do the same with the USB port.

Step 7: FINISHED

Congratulations! Now you have a portable, solar-powered battery bank made our of mostly salvaged parts! You can use it to charge your phone, tablet, MP3 player, and anything else which runs off of USB power! Bring it out into the sun and keep your devices running.

Please leave a comment if you have any questions, comments or suggestions about this Instructable.