How-to: ‘usb Battery’ V2

usb battery v2

thanks to everyone’s great feedback, i’ve now got a usb battery that’s much more efficient and capable of delivering more current to a portable device.  like i promised, i put together a slick little case to finish this hack off right.  read on for some tips on building your own.


quick improvement

as mentioned by several readers, you’ll want to use a 5 volt regulator ic instead of the resistor/zener-diode combo i discussed previously.  you’ll be able to charge your device faster while it is running and it’s much more efficient, which will give your 9 volt a longer battery life.

the best part is that it’s easier and cheaper to do it this way.  just grab an lm7805 from your local hacker store and wire it up.  connect the positive battery terminal to the 7805 input pin, the positive usb pin to the 7805 output pin, and connect the negative battery terminal and the usb ground pin to the 7805 ground pin.

which is which?  if you hold the 7805 with the text facing you and the pins downward, the pins from left to right are: input, ground, output.  it looks like this:


for the female usb connector, look down into the end of the connector so that it is oriented like so:

usb connector

pin 1 is the positive (5v) terminal (which goes to the output of the 7805) and pin 4 is ground (which goes to the 7805 ground pin).


easiest way to test

several people were wondering how to tell if you are going to fry your device.  here’s the easiest way to test when you are all done wiring:

  1. cut a standard usb cable in half.

  2. plug the male end into your usb battery.

  3. connect the positive and negative ends of your multimeter to the red and black usb wires respectively.

  4. if it reads something very close to 5v then you are wired correctly.


making a case

usb battery case 1

i chose to make my case out of polystyrene plastic.  you can find this stuff in sheet form at most hobby stores.  it’s the same kind of plastic used in your standard plastic model kit and the sheet form lends itself nicely to making flat sided objects

331 thoughts on “How-to: ‘usb Battery’ V2

  1. I’ve read in various places lately that a “switched” voltage regulator doesn’t convert the excess voltage to heat. Can anyone confirm this? And if so, point to a product that can be purchased somewhere? I’ve had a hard time finding one for sure online.

    The reason I like this idea better than 4AA is that the 9v has a much nicer form factor for a compact case.

  2. Has anyone tried this with a 12V lm7812? Was it two 9V in series to get 18V for the input?

    What about a dc/dc converter that would go from 9V up to 12V

    I am asking because I have firewire ports and I want to use them, and the firewire spec says 7-24 V and I want to stick to 12V like the 4G ipod likes.

  3. #52

    the way i would do it, is to get 2 9v batterys hooked up in series, put in a 1N4004 diode to stop reverse current on the negative side of the 9v series, and hook it up to a firewire port.

  4. i figured out where to find female usb adapters. there are a lot of those little ps2-to-usb connectors floating around because most pc vendors include them along with their usb keyboards. nobody uses them and your office tech support person probably has a drawer full of them.

    they are all encased in plastic, so it’s a bit of a chore removing the usb connector… but they are free and in good supply.

  5. All someone has to build now is a box that charges, and can be charged as well.
    It could have an input on 1 side and an out put on the other, with a rechargeable 9v battery in the middle. That would be cool… then you would never have to replace the battery and could seal the unit to stop any of the wiring getting damaged.

    Anyone brave enough to try it?

  6. Just built my own. A really entertaining project. For mine I used an Altoids tin for the box, same as the firewire battery pack. I made a small modification. I used two 9v batteries, the first directly connected to the 7805 for 5v USB output, then I connected that 9v in series with another and used that as input into a 7812 for 12v Firewire output. Both ports work great, and I connected the voltage regulators to the outside of the tin for heat dissipation. If anyone would like to see some pictures, let me know, I’ll email to you.

    reeselloyd (at)

  7. G’Day !!!

    My hearty congrats for thinking out a marvellous project and presenting it so very very well.

    Anyone could make this, thanks to your easy to follow instructions.

    It is a pleasure to see the human mind in action and it just goes to show that in the year 2005, not everything has been invented.

    Thanks for an intriguing read and for sharing it with myself and others!

    I have bookmarked your site and it now occupies a place on my link bar too !

    More projects please !!!

  8. hi keith. they’re called breadboards. they basically just let you easily connect components together without having to solder them. it’s a nice way to test and experiment with a ciruit before spending all the time soldering it together.

    you can pick one at a radio shack or just about any electronics store that sells that sort of stuff.

  9. re 43, USB power is switchable.

    Try plugging the shuffle into a powered hub, with its upstream disconnected: the shuffle won’t start to charge until the upstream is connected to a USB host. Many hubs will indicate this by changing the status LED in some way.

    Similarly, you can power-cycle attached USB devices by resetting the USB controller; in linux you can do this by rmmodding the USB modules.

    That the power doesn’t come on unless it’s connected to a computer was an issue when testing my USB christmas tree – there’s no real way to see if your USB device will work without damaging the computer unless you connect it to a computer. I suggest using a cheap computer.

  10. I’ll be putting another charger up as soon as my supplies come in, I’m going to try them a few way- with and with out buy it now. I was surprised at how quickly it sold. esp. since the additions were pretty darn simple.

  11. I found USB female connectors on for $0.35 each. they are part number 154-2742 all I could find were right angle connectors, whatever they worked! It took a week to get them and the rest of my parts for the 10 chargers I made for ebay.

    Making one of these was easy but it was 2nd nature by the time I got to number 10.

    I’m thinking of setting my roommates into slave labor and manufacturing these in our kitchen!

  12. a number of people have commented on the fact that to charge the shuffle you have to tie the other pins to ground, but I was wondering if this affects the charging of the 4g ipod. Anyone know about the charging pinout of the 4G with usb?

  13. re #70

    I don’t think its possible to the big ipod through usb.

    re #68 and others,
    It should be possible to use any supply that provides 5v or more. so 3 * 1.5v in series wont work (4.5v) but 4 * 1.5v should (6v)

  14. I just made one of these (I put it in an altoids tin also) and it works wonderfully with my iPod. What is the best way to hook up 2 more 9v batteries? Series? I need to keep the stuff in the tin in place anyways, these batteries will keep it nice and solid.

  15. I bought an iPod Shuffle, which due to a design flaw by Apple doesn’t work terribly well with certain Macs–namely the USB plug is too short to fit into the high-powered USB port and get charged up (luckily you can sync your music on the low-powered port, but the battery slowly dies). Now you could go out and buy a USB extender, but that’s lame and dull, especially if you already have another iPod that comes with a handy wall-charger.

    But that charger outputs to Firewire, not USB. So here’s the question– could I solder up a cable that would be Firewire male on one end, and USB female on the other for the express purpose of charging up my shuffle? Pin 1 to Pin 1 for power, and Pin 2 to Pin 4 for ground? It’d be great while on vacation in areas where you don’t have access to USB ports, and you haven’t got around to making a battery-powered USB box…

  16. 73: Yes you can. All usb and firewire cables do is conduct electricity. By simply splicing the two together, you can make it work. Just splice it right with no shorts though. But if you do, I be happy to take your dead iPod for you…

  17. This was an awesome project. with regards to post #8, anyone ideas on connecting the “National Semi switching regulator” to double battery lifetime and gettin rid of excess heat? is this part larger? and how much more would this part cost?

    My shuffle is definately happy :)

  18. I just made one with four AA’s. Works NICE! I would definatly reccommend making one. I have a nice case that I made a sliding door with for the usb port. The only problem about the AA’s is size and that isn’t really too big an issue, what I have is about as big as a 20 gb iPod. I havn’t tested battery life but I will tommorow and get back to you guys Thursday.

  19. I just made one with four AA’s. Works NICE! I would definatly reccommend making one. I have a nice case that I made a sliding door with for the usb port. The only problem about the AA’s is size and that isn’t really too big an issue, what I have is about as big as a 20 gb iPod. I havn’t tested battery life but I will tommorow and get back to you guys Thursday.

  20. I just made one with four AA’s. Works NICE! I would definatly reccommend making one. I have a nice case that I made a sliding door with for the usb port. The only problem about the AA’s is size and that isn’t really too big an issue, what I have is about as big as a 20 gb iPod. I havn’t tested battery life but I will tommorow and get back to you guys Thursday.

  21. Sorry about the triple post. Correction to my last post, I just killed my iPod mini with it. I think its cause i used up my iPod battery all the way so it had to be booted by the usb battery… The apple symbol flashed a little and then it showed the low battery sign. Gotta love warranties.

  22. i have a sprint sanyo 8100 phone and i would like to make a usb batt for it. my question is… can i make the same above mentioned batt. except use a MALE usb end to connect to my phone’s female end?

  23. Can i use this same setup but with a different type of connection, other than usb? i have a sanyo 8100 sprint phone that has two different type of connections, one is a regular ac/dc jack for the wall like in cd players, and the other one looks like a usb but might not be. need help please, new to this.

  24. Just built the box and it works well. But it doesn’t seem to charge a 40 gig iPod photo through a usb dock cable. The iPod charges when the usb dock cable is connected to my computer, however.
    Has anyone else tried a big iPod with their usb altoid box? Does it charge?

  25. so can you play music on the shuffle while using the charger? somehow i don’t think you can (probably has to do with the two data lines that are tied low, i’ll have to read the USB spec to verify). apple’s battery pack allows you to play music while using external power. i think it might have to do with special signals, probably on the extra USB pins on the shuffle (

    if you can’t play music, why not cut the battery out and simply connect a USB connector to a 5V DC adapter. it’ll serve as a nice travel charger. no need for replacing batteries, finding enclosures, or soldering. i’m gonna try to build one soon.

  26. 1) can this provide a strong enough current to charge the ipod mini (2nd gen)? also, how long can a 9v battery charge it for?

    2) im interested in making a circuit that could charge a rechargeable 9v through usb when connected to a computer. is that possible?

  27. 86: I believe the extra 5 pins on the usb might be for programming the onboard chips post-production, i.e. add the bootloader/firmware after constrution of the shuffle since it might be easier, faster, and alot cheaper. It would have nothing to do with the normal operation as standard usb only have the 5 pins (v+, V-, d1, d2, shield).

    Someone needs to buy a charger and crack it open then report back.

  28. mulcbone, yes you can use that cable, has a nice 1394 2×5 pin diagram. however for my purposes (to create a battery for ipod mini) i need to actually have a female 1394 connector attached to the battery…

  29. Seems nice :) Will try this as soon as my new Ipaq arrives (somewhere next week).
    Two questions though:

    *while reading throught the datasheet of the 7805, on page 21, figure 8 “fixed output regulator”, there are two capacitors used in addition to the ic. Are those useful for this purpose? I’ll be adding the diode anyway so would be just a little extra work…

    *I’ve got a Sony-Ericcson cellphone which runs at 3.6V, would there be a way of using a 9V battery to get 3.6V? Adding a resistor perhaps? Or would a DC/DC stepper be something that works? Are those expensive? I’m quite starting at electronics, but it should be possible,right?

  30. I’ve made an improved version with a switching voltage regulator and a output indicating LED. All testing were done on a Palm Tungsten E. These are the parts I’ve used.

    – 78SR105VC
    Fully integrated switching voltage regulator from texas instruments / power trend. By far the most expensive component (US$18). There are other cheaper options (search the national website), but they tend to be much larger or requires external components.

    – 1A Schottky diode
    This is connected on the input to protect the voltage regulator from reverse current. It won’t tolerate a very high reverse voltage, but with a low voltage drop it should allow slightly more power to be squeezed out of your battery.

    – 1uF multilayer ceramic capacitor
    I put one each on the input and output of the regulator to reduce the noise. Not sure if I really need it, especially on the input, but it’s cheap and small so why not?

    – 4V Blue LED and 2V Zener diode
    This is the tricky bit. As the current required by the LED is pretty low, you can connect these two across the 5V output and still get enough current to light the LED. Voltage drop is around 1.7V across the zener, and 3.3V across the LED. When the battery gets flat, the voltage output will start to drop, and the LED will shut off around 4.5V on the output, letting you know it’s time to change a battery.

    If you are just using a resistor and an LED, this will not work. The output voltage will have to drop much more before the LED turns off. Your equipment will likely stop drawing current well before that, greatly slowing the rate of voltage drop. It’ll probably be hours from the time your equipment stop charging to the time the LED turns off.

    Note that due to the low current, you’ll be working well within the non-linear region of the diodes. It can be quite hard to determine the right combination of LED and zener, and was pretty much trial and error for me.

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