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. This guide really is made for the below average idiot with articles such as ‘how to tell if you’ve done it properly’. If you need help testing it out with a multimeter, you shouldn’t really be doing this.
    Anyway… Great article non the less. I think the use of a voltage regulator was well adviced and it would be nice to see everyone elses attempt at this.

  2. It would be even better if piggy-backing was added, so you can just plug the battery pack into another USB device (like a hub) so you can also manipulate the data on the usb device (ipod, phone, etc)

  3. Very nice. Mostly impressive was your good attitude for taking the heat on so many “bombs” and comments about the zener issue. I was going to be one who suggests using a low voltage drop regulator, but I thought that you had enough from others. Again: kudos for how you took the feedback and how you built this USB v.2 :)

  4. if it’s plugged into a powered hub or computer, isn’t that device going to be providing a charge anyway?

    nice writeup, very impressed with your top-quality styrene manipulation. all kinds of pro.

  5. Not bad, I would replace the 7805 with a National Semi switching regulator (or similar), though. The 7805 drops the excess voltage as heat. So, you’ve got a 5V USB device running off a 9V battery. The 4V difference is being dissipated as heat. If your device is using only 100ma, then you’ve got: 4V * 100ma = 400mw being wasted.

    With a wall-wart supply where power is “endless” this isn’t as important, but with a battery, where your total AH (amp hours) are fixed this is a concern. A switching voltage regulator only needs a couple of extra components, but will probably double your battery life.

    Overall, a cool idea, though.

  6. Seems to me that this idea and this general line of products are going to be increasingly more important as our portability increases. What do you all think about a device that could charge anything, maybe using a 12V lead-acid battery like used in UPS power supplies. I think they are 7 Amp-hour. This would be enough to charge a laptop, maybe an ipod, cellphone, etc. Actually though I’m looking at moving everything over to a treo handheld and a powerbook for my portability. So maybe I’ll make something like this for the treo, probably use the national switching regulator though. Any one built a battery system for a powerbook?

  7. A few thoughts in no particular order:

    I have a Treo 600, as do several people at my company. It can usually go a full workday of HEAVY use before in danger of needing a recharge. Not sure of the ROI on making an external battery for it, unless you plan to do continuous shoutcase streaming or something.

    Lead-acid batteries are HEAVY (ref: the “Lead” portion of their name ;) ). Yes, it’s easy enough to take an alarm battery and use it in this manner, but a 6V cell with a similar AH rating would be ~ 1/2 the weight. That coupled with a low-voltage regulator would be a tad more portable.

    Even better might be to look into the “Batcap” line of car audio capacitors. These are like hybrid batteries that can charge faster than a normal battery (more like the almost-instant charging of a traditional cap), but they also seem to hold that charge longer. The idea would be to make a power charging “rig” that when you are near power (AC or 12DC) your portable devices and the batcap all charge, then later you can switch to using the batcap, or other battery, to recharge the portable devices.

    I have found that it’s usually not too hard to find an outlet, though. I don’t *personally* think it’s neccessary to carry around a bulk supplemental battery, but I am sure everyones needs are different.

    Does the powerbook have removable batteries? Unles you ABSOLUTELY need the continues runtime it would be much easier to just carry a spare battery, this has been my solution with Thinkpads for years…

  8. First, you would need an exteral recharger Sebastien.

    Second scott, noone wants to void their warrenty, or if they lack a warrenty, why risk the powerbook?

    Wouldn’t there be a way to halve the 9 volts into a 4.5v charge with twice the wattage going thru the system? Then instead of needing a voltage dropper, and wasting the battery, you just get a small dc-dc stepper to up the 4.5v to 5.0. It would take a little bit of soldering, but it would make charge time double (I think) while not wasting battery power. Or you can just use 3 aa batteries with the stepper, or 4 with the 7805, as 50mw loss isnt that bad.

    Anyway, israel torres gave me an idea. A portable, cable-less usb hub power supply for when you need that extra boost to power 4~8 usb flash disks….

  9. I assume by ‘#3’ you mean post 3, well that’d be me. Well something as simple as checking the voltage of a circuit I learned in first year in secondary school a long time ago. I’d assume that something similar has been taught throughout most other education systems.

  10. As a previous poster indicated, the 7805 will dump the excess voltage as heat.

    However, a 7805 is damned cheap and readily available. If you are going to use one, go with 4 AA batteries. That will produce 6 volts, waste less energy as heat and likely provide more run time per battery set anyway.

  11. Ryan
    You would be wrong. Most US schools (On the east coast) only have vocational classes like electronics in high school, while some might in middle school, but both are electives that the student would need to want to take.

  12. Referring to post #14 (Ryan): They don’t teach that sort of thing in high school right now as far as I know. There may be some of that multimeter stuff in a few of the voc ed classes, but I’ve been too busy with science, math and English classes to take any sadly. Even if they did, it would only be in maybe one class period of construction trades in our tiny school (note that my high school is really small). Still… I guess high school just isn’t what it used to be. Ironically perhaps, everybody blames “no child left behind”. :)

  13. i love the case ! don’t know why i never thought
    of it, seems like i learn something from every
    post ! soon i will be able to take over the
    world !
    well after i make boxes for my ir remote blinds,
    voice activated toilet flusher and usb thumb print fridge lock :-)

  14. Very cool project!

    I don’t know if it’s worth taking the hit as far as increasing the size of the unit, but it strikes me that it would be very cool to have a rechargeable battery that is maintained automatically while the pack is plugged in to a USB outlet.
    That way you also have an excuse for a data pass through as well, so you wouldn’t lose a USB outlet and the battery pack is always ready to go.
    One could maintain multiple batteries in an inline arrangement that way too.
    One could also leave multiple packs connected for increased running time.


  15. in response to posts #14 and 17

    you could employ a simple voltage divider circuit with two resistors of equal value, though they’re going to be a constant drain on the battery when not in use. By splitting the 9v in half this way, you could have 2 USB output terminals, but not one with twice the potential power output. You may want to parallel 2 9v cells in that case though.

  16. 13#
    i agree with that, im a student and Most of the How 2 sites and Hax sites use language that is much too advanced for the avarge reader. this article was writen well and explained ALL THE NECCORY DETAIL. Good article gys i will be bulding my own when i can get stuff

  17. #22
    Most how to sites don’t use advance language, just relative to the project. If you cant understand how something is built, go learn about it first.

    Also, most of the stuff on here arn’t hacks per-say, they are mods. Hacks require code….

  18. i always thought of a hack as making something do something that it was not intended to do.
    hardware or software. we need a forum to help
    each other out because its to hard to check on old posts.

  19. Someone on the other usb-battery pack has mentioned that the shuffle and the ipods (mini included) might include a dc-dc stepper. Though I rather go with the standards for the connections, this would be useful in creating more simplified circuits.

    Also, #29, the charge times at the same volts and amps for the shuffle as the regular computer connection would lead to the same charge time. So 5volts at 1amp usb or battery pack would equal the same charge time.

    And Dan, Hack would mean more to completely change something to do what you need. Mod(ification) would be to slightly change something. Most stuff here are mods. Or inventions, as most stuff like this usb-battery would be made from scratch, yet designed to be like something else. Which, if I might add, is the best among the three.

  20. Awesome Hack, an add-on that I’d like to see would be a recharging circut, so you could use a rechargable battery and recharge the whole unit through usb from your computer.

  21. #22
    A resistive divider makes a very poor voltage regulator unless you have a constant and known load. Basically the device being charged has to be considered as a resistor parallel with one of the resistors in the divider. In the case of a charger I would say a constant load is the next best thing to impossible , as the device charges the current draw will decrease and the resistance of the charging device will increase.

    A linear regulator as used here is the simplest most bulletproof solution. A switching regulator as several have mentioned adds complexity but should waste less power.

    V=IR P=IV
    V=Voltage(volts), I=Current(amps), R=Resistance(ohms), and P=Power(watts).

  22. going to try this, i can pick up the regulator for $1.20 AUD and the other stuff cheaply, now lets hope the shuffle does not come with an added security measure, eg does not charge unless signaled by the pc its connected thing.

  23. I was wondering something with this project. Apple, as an accessory to the iPod Shuffle sells a 120V – USB adapter to charge the internal battery. What if you used a female-male converter and a rechargable 9V? Could you charge your home-made adapter without ever having to remove the battery?

  24. Hi,

    I built the LM7805 version, which works, but gets red hot when charging my Sonyericsson phone.

    I’m thinking of making the switched regulator version so that I don’t need a heatsink.

    What regulator could anyone recommend?


  25. 37. Post
    if u are going to put the charger into a box, have u tried using a tin box and connecting the regulator to the tin box with a screw and thermal grease? also add a diode that stop current going the wrong way, might help u not fry the regulator if the terminals on the battery touch the wrong way.

  26. has anyone used this with an iPod? if so, what type of results are you seeing concerning the 9V battery life? are you using it to charge the iPod? if so, how much long will the 9V charge the iPod?

  27. #41 its kind of weried the results i am getting with the shuffle. it seems that when i plug it into the 9v charger the green light blinks, saying its has power. the battery status light, lights up but does not blink,

    but when i put it in the pc, nothing happens until windows picks up that a device is plugged in,


  28. i got a ps2 slim, when pluged into that it instantly goes into do not pull out mode, eg amber flash. i do not have an u powered usb drive or hub, i do have 8usb ports on my motherboard.

  29. thanks that does the trick :) btw have u ever check how hot the regulator gets?

    also u should add a switch so that u can turn the charge on and off, eg have it has a external battery or just a charger.

  30. Has anyone tired this with a 12V solution? What size batteries did you use to get above 12V for the lm7812 and would it be possible to take a 9V battery and use a dc/dc converter to go from 9V to 12V? (i bought firewire connectors and don’t feel like buynig USB ports to get the 5v, and I would like to use a regulator and not just hook up a 9V battery to my 4G ipod)

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