Build a Battery Powered USB Charger





Introduction: Build a Battery Powered USB Charger

This guide will walk you through building a battery powered charger for any device that charges via a standard USB connection, for example cell phones, iPods, etc.

Parts Needed:

1. 9V Battery
2. +5V (.7285) Fixed Voltage Regulator
3. Project Case (4x2x1")
4. USB Male A to Female A Cable
5. 22-Gauge Hookup wire
6. 60/40 Rosin Core Solder
7. 9V Battery Snap
8. 9V Battery Clip

All Items can be found at RadioShack

Necessary Tools:

1. Glue
2. Soldering Iron (with a fine point)
3. Soldering Iron Stand
4. Dremel Rotary Tool (with appropriate cutting disc)
5. Wire Strippers
6. Wire Cutter
7. Forceps
8. Safety Glasses
9. Screwdriver (Phillips)

And now, a few safety precautions:

1. Wear safety goggles while operating Dremel, pieces of plastic or dremel disc may hit your eyes

2. Choose a well-ventilated space to work, as fumes from soldering are hazardous to your health

3. Do not touch metal parts of the soldering iron while working, it will be very hot

4. Place the soldering iron securely on a stand, do not touch your table, clothing, countertops, or other things you do not want burnt or melted with the tip.

5. Do not touch the voltage regulator, it operates at near 150 C (302 F), it will burn you if you touch it.

As soldering skills are required for this project, if you don't already know how, this link from Make Magazine provides a good tutorial on soldering:

Total Cost: about $25

Time to Complete: approximately an hour

Step 1: Preparing USB Cable

Cut the USB cable down to size, leaving approximately 1 inch of cable outside the plug.

Strip the insulation from the outside of the usb cable to expose the red, black, green, and white wires inside

Strip the insulation from the red and black wires, red will be our (+) and black will be the (–) connection to the regulator.

Step 2: Case Preparation

Cut a hole in the side of the project case that approximately matches the size of your USB plug.

• Outline the usb plug with pencil on the outside of the case.

• Cut away the plastic using a Dremel or similar rotary tool.

• If your USB plug is rather large, like the one we used, you may need to cut away some of the lid, do this in the same fashion as above.

Note: If you have the means to do so, it may be easier if you clamp the project case to a work surface to hold it steady while you cut.

Step 3: Battery Snap Wire Preparation

Strip the wires from the battery snap to expose a greater soldering surface

Step 4: Battery Clip Mounting

Place the battery clip in the case using glue.

For our case size, we chose to mount it on one side of the case.

Depending on your case size (if you choose to use a different one), you may choose a more fitting location.

Step 5: Prepare the USB Power Wire

Cut two lengths of 22 gauge wire (in our case, just over an inch each).

Strip the insulation from both ends of each wire to expose enough for soldering.

Step 6: Soldering the Battery Snap

Solder the red battery snap lead wire to the (+) end of the voltage regulator and the black lead wire of the battery snap to the (-) end of the voltage regulator.


Ensure you do not cross wires during the soldering process as it will short the connection.

Do not hold the soldering iron to the voltage regulator for extended periods of time, as prolonged temperatures of 150+ degrees C will damage the regulator.

The tutorial mentioned in the introduction page about soldering can be found at this link:

Step 7: Solder the USB Power Wires

Judge how your wire will sit inside the case, and bend the wire in the direction it will need to go to connect with the USB cable.

Solder the first length of wire, one end to the (+) terminal of the voltage regulator and the other to the (+) (red) USB wire.

Solder the second length of wire, one end to the (-) terminal of the voltage regulator and the other to the (-) (black) USB wire.

[Helpful Hint] – forceps may be helpful in holding the wire while soldering

Step 8: Assembly

Place everything into the box

(it may take some effort to get everything in the box at first, keep rearranging as necessary)

Place the lid on the box and screw it down using the four included screws.

Note: it is recommended that you do not leave the battery connected when not in use as the regulator will get extremely hot. To counteract this, you may install a heatsink on the regulator, which should reduce the temperature.

Step 9:

Charge Your USB Device!



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    Warning: This may fry your phone/devices.

    I can't find any such thing as a .7825 regulator online, but if you connect an LM317 (as shown in the photo) in this way I'm pretty sure nothing will happen. Possibly the OP was thinking of the LM7805 which would give 5V but also not if wired this way. looks like a much better start.

    i want help in 2 points :-
    1). If i dont want to remove battery when not in use.......
    2). If i want to use it as powerbank and directly charge it and reuse......,

    plzzz help

    I tried connecting directly without soldering. it didn't work, is it compulsory to solder for it to work.?? pls reply

    You shouldn't need to solder for any project to work. As long as it is making contact, it should work. However, this project is just wrong, as the 9v battery is directly connected to the USB female port, so you would be feeding 9v to your device which could easily damage it.

    Simple and neat. Version 2.0 of this would be to include a battery charger circuit and use LiPO battery pack to source something like 6000 mAh. These are readily available for around $30, so would be good to calculate the cost of building one yourself. This then can be used to supply multiple boards (like RPi, Arduino etc.) simultaneously. Not sure if these 9V batteries cross 1000 mAh ratings. Another option would be to use AA NiCd or NiMH that are rechargeable and can provide around 1000 to 3000 mAh. There is always a tradeoff between cost and efficiency. :)

    can we use any other device like resistors instead of voltage regulator

    how can i charge the power bank... can i directly charge with the electric charger..

    Hello everyone... i love what happens here on Instructables. I love building up stuffs like this cos i use an Android device and the battery seems to drain very easily. Pls i have a charging project i want to do. Can i talk to anyone to help me out with how?

    Why hasn't this project been corrected? It is a travesty and irresponsible to leave instructions that could lead to frying someone's electronic equipment!

    DO NOT USE THIS CIRCUIT AS SHOWN! Having wrong information for the public is worse than nothing at all!

    dwoods-1 is correct you WILL damage anything which requires 5 volts with these connections as you WILL be supplying 9 volts directly.
    I cannot find any reference to a .7285 regulator but a 7805 would be fine.

    Looking at the diagram you provide you need to connect both black wires to the centre pin. Connect the red wire from the battery clip to the top pin and the red wire of the usb cable to the bottom one.

    See this diagram: