How to make a external cell phone battery for under $10

The intro will just explain one thing: why I decided to make this.
When I go on long trips, I like to be prepared. I also like to listen to music (when awake on that trip.).
Recently, I got a Android smartphone, and like all smartphones; the battery won't last more than eight hours.

This summer (2013) I am going on a 14 hour bus ride. So there's my problem: Too little power, no job,  and real external battery packs cost upwards of $50. 

So, I made my own; with a bit of help from the fellow evil scientists of the internet.
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Step 1: Parts.

To build this pack, you will need:
-A brain, some logic, and common sense.

- A "size D" four-battery case.

-A pack of Diodes.

- A USB cable to your device.

- A multimeter.

- Extra wiring (just in case).

- Electrical tape.

-And of course, size D batteries.

All of these things (besides the first) can be found at a hobby store (such as Radioshack).
If you feel a little uncomfortable jumping into this, check out this Instructable on some basics.

Step 2: USB cable and wiring.

The first thing is to make the adapter for your device. If it's a iPhone 5 or an Optimus G, the process shown here applies. So, take the cord for your device and cut it about half way. You can always cut it shorter later on, so it's a good starting point.

Once you have cut your wire, strip each smaller wire inside of it. Proceed to next step to find which are the power cables.


Now, with the USB male half of the cable plugged into a USB female power source, test two of the wires at a time with your multimeter to find the Negative and Positive wires. 
I actually recommend doing this from a USB outlet adapter, because if you end up shorting this don't want to have to buy a new laptop.

Generally, Red is always positive (+) and black is always negative (-), but it's a good idea to test and not just assume.
dasimpson198110 months ago
some phones need these wires connected with resisters to indicate to the phone it is pluged into a charger
The Dark Lord (author)  dasimpson198110 months ago
Hmmm...I didn't know that. Point taken, although this setup works for my relatively new phone.
lucky break then
They have 50,000 mah external batteries on eBay for $20. I'm going on a school trip to DC in the spring and am going to charge peoples phones for money, I don't expect to make much but hopefully I can make some extra cash.
Gilik8 months ago
Nice instructable! which app do you use for the notification of battery charging?
The Dark Lord (author)  Gilik6 months ago
Sorry for the late response, but to answer your question;
"Battery Widget Reborn".
hfdjgl10 months ago
you should use a power source closer to 5 volts
The Dark Lord (author)  hfdjgl10 months ago
I should, it would be ideal; but this was the best I could find in Radioshack. I didn't have the time to buy online either.
dasimpson198110 months ago
ah you need the resistors on the usb data lines most new phones do now
The Dark Lord (author)  dasimpson198110 months ago
This charger was made for the sole purpose of charging the phone. The wires for data transfer inside my USB cable are completely ignored and cut away.
dasimpson198110 months ago
why do you have the diodes
The Dark Lord (author)  dasimpson198110 months ago
My phone won't recognize it's charging without them; most likely because it wasn't without them.
I only had it plugged in for less than 30 seconds, but I didn't want to to risk a $500 phone over a simple experiment (turned instructable).

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