For a long time I've had old back up cell phones taking up space in my desk drawer. I was curious if I could put any of these old phones to some use. I can't just throw them away so I decided to try and re-purpose one of them as a portable charger for my current smart phone.

Step 1: Materials

Mp1405 5v 1a Lithium Battery Charging Board (Blue board)

http://www.amazon.com/gp/product/B00EXGFG42/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

2. DC 3V to 5V 1A USB Battery Converter Step Up Module (Red board)

http://www.amazon.com/gp/product/B00C93Z8JY/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

3. SAMSUNG OEM EB-L1D7IBA 1850MAH BATTERY FOR GALAXY S II

(If you don't own a Galaxy S II)

http://www.amazon.com/gp/product/B007PSBELE/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

4. 4 jumper wires ((2) 1.5 inch wires, (2) 2.5 inch wires)

http://www.amazon.com/Pre-formed-140-piece-Jumper-Wire-Kit/dp/B005GYB93M/ref=pd_sim_t_3?ie=UTF8&refRID=1CT2Q151JM4F5PDK7Z1A

Tools

1. Soldering Iron

2. Solder

3. Access to a 3D printer

Step 2: Circuit for Charging Portable Battery

Insert and solder the two 2.5 inch wires to the B+ and B- terminals of the "Mp1405 Charging Board". Each of these wires will be connected to their respective positive and negative contacts on the battery. The "Mp1405 Charging Board" is what will be used to charge the cell phone battery, and will feed power from the battery to the "DC Converter Step Up Module". The Micro-USB connector on the "Mp1405 Charging Board" will be used to charge the internal battery of the portable charger.

Step 3: Circuit for Charging Smart Phone From Portable Battery

Using a 1.5 inch wire, connect the OUT(-) terminal of the "Mp1405 Charging Board" to the IN(-) terminal of the Converter "DC Step Up Module". Do the same thing with the OUT(+) and IN(+) terminals. The USB connector on the DC Step Up Module will be used to connect a micro-USB cable in order to charge a smart phone.

Step 4: Setting Up Battery Pack Internals

Download the STL files at the bottom of this step, and use a 3D printer to create the case for the portable charger. Once the case has been printed carefully insert the charging boards and thread the two larger wires (attached to the B+ and B- terminals of the Mp1405 Charging Board)through the two holes in the case. Make sure the wire connected to the B- terminal is fed through the bottom of the left hole, and the B+ terminal is fed through the bottom of the right hole (reference of left and right holes is based on the second picture from the top). Once both wires have been fed through the bottom of each hole, bend them back so they are fed back through the top of each hole. This way each wire will not move when the battery is inserted, and the positive wire will touch the positive terminal of the battery and the negative wire will touch the negative terminal of the battery. Make sure the two wires do not touch each other.Then slide the battery into place.

If you are uncomfortable about the wires possibly crossing, you may be better off soldering them directly to the contacts of the battery.

Step 5: Finishing Touches on Case

Once the battery is in place, slide on the second half of the case. There are a series of cavities on each half of the case, to make sure the two halves fit exactly together. Next put the cover on the front of the case, to cover the two wire holes. To make sure the case holds together, use an adhesive like Sugru.