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. Hi. I have made this from parts on maplin, and added the ability to use a usb power input (cigar lighter adaptor thing). It has 2 output ports, and when i plug in my zen touch, it turns on (like plugging it into the computer), but then when i turn it off it just turns off (when on the computer, it charges). Anyone know? This is really annoying. Thanks :)

  2. would this same setup work to power or recharge a ZEN micro?

    my son bought a zen micro on ebay, but this set up didn’t come with a power adapter. #$%^#$%^!!! It will power and recharge through the usb, but i was wondering about just cutting off the end of a usb mini 5 pin and hooking up the positive and the ground to a 5 volt, 1000 mA power adapter. Would that simple type of connection work? or is there more to the usb wiring than that? Or are Zen micros too new to know anything about that yet? just curious, trying to find a way around having to spend $30 extra bucks…

    Thanks in advance for any help.

  3. does anyone know where you can buy JUST the mini-usb connector (preferably with soldering contacts)? I’ve googled til I’m blue in the face but can’t find a retail supplier!


  4. Does anyone kow if this hack will work with a Nokia 5100 series cell phone. The cell phone battery is rated at 3.6v DC and the wall charger supplies about 9 volts DC at no load. I am thinking that I could use a pigtail wired to the the LM7805 and 9v battery (or 4 AA cells) and plug the end of the pigtail coming out of the box containing the battery and VR into the cell phone charger socket. Question is, would the 5v from the regulator be enough to charge the cell phone and not overcharge? Thanks for any help. Emergency use of course.

  5. #205> I think it would blow a circuit, but what’s the rated cell phone current flow?

    Oh, I did this hack and for some reason it won’t charge my ipod mini. I check with my voltmeter and it’s abot 5.06v through the USB. The iPod turns on when I plug the usb end in but it does not charge. Is there enough amps flowing through for the ipod to charge?

  6. i know absolutley nothing about any of this, but nontheless i want to give it a go. i have a 4th gen 20gb ipod. could io make a usb charger rather than a firewire one?

    it has been mentioned that to make the charger, a “lm7812 12v regulator” is needed. are either of these what is needed?:

    i’ve got the female usb connector from an extension lead so thats ok. a 5.1v diode is listed under what is needed, would a 5v one do? i’ve got a 330ohm resistor.

  7. ok, i just finished the charger last night. i put it into a small plastic box from maplins. the only problem is the heat from the lm7805 is a lot and started to melt some of the inside of the box where it touched off.
    does anyone have any ideas of how to stop it melting the box?
    at the moment the power in is a 9v battery with 8.1v left in it and the output from the charger of 5.1v.

  8. I did one power supply using a 7805 and a couple of capacitors, it works great for my Ipod and Motorola m500. To feed the Motorola you DO need a heatsink on the 7805. Also made a 12v to 1,5v (car use) for the Muvo Tx FM (1,5 rated) using a LM 317. Works great also.

  9. Adding comments to 209: even with 2 capacitors (one in the input 10pf and another in the output, 10uf) I got a lot of noise when using in my TLC (diesel engine). But I put both dc-dc converters in a plastic box, and common wiring for both. Gone to get some filters and solution.

  10. awesome idea. if you were to use a rechargeable 9v
    how would you wire in a jack to charge without dissconnecting battery. would you use a diod so it wouldn’t backfeed into the rest of the circuit?

  11. Hi, i just assembled the circuit using the LM7805 about 10 minutes ago. First I used a car mobile phone charger that gives out a voltage of ~8v as the power source and when I hooked my shuffle to it all that happened was the green led on the front came on and disappeared after a second or two, and when i pressed the battery test button the indicator flashed green for 3 or so seconds and then went out. Then I tried hooking up the 12v source directly to the regulator (2.7AH UPS battery) and the result was still the same. I was afraid the shuffle was busted but it still works. what am i doing wrong?

  12. i am currently making one, with a 7805, a usb female, and a 9v battery alone.. didn’t quite test the circuit for a long time but out of curiousity, how much will the 7805 ic heat up by? i’m at the point of making a casing for the circuit now…

  13. Don’t want to get too complicated here, so i’ll try and keep it short.
    In order to find out how hot something gets in air (no heatsink) you need to know Tjc (Temperature coefficient junction to case) and Tca (Temperature coefficient case to ambient)
    For a LM7805 regulator TO-220 package Tjc is 4deg C/W and Tca is 50degC/W
    So the total is 54 deg C per watt.
    So for every watt you disipate the temperature of the juncion (the silicon inside the regulator) will rise by 54 deg above the ambient temp.
    For a linear regulator you will dissipate the volts dropped across the regulator times by the amps through it, so if your ipod draws 100mA from this device you’ll drop 4V (9V-5V = 4V) which makes for 0.4W (4V * 0.1A = 0.4W) The temperatur of the junction will be 21.6 degC hotter than the air.

    However since the air is enclosed it will heat up tooso the ambient temp wil increase. Say (for instance) that the air temp reaches 50degC this will mean that the junction temp is 71 deg

  14. I got to about post #100 before I skipped to the comment section. LM7805 is great for this type of charger!!! Unless these people can make their own printed circuit boards, a switching regulator is a stupid recommendation. An smps would be great, but thesepeople aren’t EE’s.

    I want to charge my iPod mini while being able to play music. Any ideas?

  15. Hey, an idea for the case. In DT (design and technology) we are doing acrylic stuff at the moment. White acrylic looks really cool. If you have a strip heater (or a nice DT teacher) then you could make (i don’t know how to explain this) a u, and then a table. (argh how to explain without drawing it). White acrylic looks very iPod-esque… downside is it scratches a la ipod nano white; ipod 5g white.

  16. Does anyone know if something like this can prolog the ipod’s internal battery’s life expectancy? I was thinkin that if I used the external battery all the time and kept the internal ipod one from discharging, I wont go through any charge cycles at all. or would I?
    does anyone know where the ipod draws its energy from first? internal battery or external supply?
    btw wat voltage should I use for a mini? and can I use two of those 3.6v rechareable battery packs connected in series?

  17. I’ve tried lm7805 with my nano. Works great. Did not ground the data pins (2,3). I was able to charge the nano and listen to music at the same time. I’ve got a long plane flight in Dec so this will come in very handy.
    Matthew, an smps is a good idea. They do not loose as much power as a linear regulator. Cooler running and the battery will last longer using a smps.

  18. Dumb question time: What is the purpose of dropping the Voltage? The back of my Ipod says it will take 5 to 30 Volts DC at 1.0 amps max. Why not just run the full 9 volts to the Ipod through a fuse or other current limiter?

  19. Found this site…


    that sell switching regulators. They are very close to the size and shape of a normal LM7805 but with up to 95% efficiency. In other words they run cool with no external cooling necessary and the battery will last longer. No external components needed so you can use the same setup that Mr. Striegel uses. The only downside is no overvolt protection and price. Overvolt protection is not really a concern in this type of cct. They cost almost $10us + shipping. I ordered the 7805sr and 7805srh. The only difference between the two is one is vertical and the other is horizontal. I’ll get them in a couple days so I’ll try them out and let you know how they work.


  20. I put together a replacement wall charger (via USB) for my iPod mini a while back, but was revamping it today. While looking for info, I came across this site, and just have to say that it’s good stuff.

    Originally, I was using a spare power adapter rated for 6V at 600mA spliced to the red and black wires to the female end of an USB extension cable. It worked, but I eventually got worried about irregular specs and decided to change the adapter.

    The current adapter is rated for 5V at 140mA, so now the voltage is more exact, and the amperage is much lower. However, now I wonder if the amperage is too low. It seems to charge fine, but I still wonder.

    So, I guess there’s two reasons for me commenting. First, to ask if someone knows the proper amperage for the iPod on USB (firewire would be nice too). Second, to tell my experience in case it helps someone.

  21. I’ve got the switching voltage regulator and have tried it out. It works. Not sure how efficient it is. The data sheet for the 7805sr says at 9v input it is about 92% efficient. My meters show an output of 4.97v, 145mA.

    The thing I like about this charger is that you can listen to music while it’s charging.

    If you are going to get a switching voltage regulator and you live outside of the USA then I suggest going to this site instead,, as they charge less for shipping. Parts are about the same price as the site I quoted above in post 228.



  22. Great “hack”. Went to radio shack bought everything I needed under $15 (including premade case #270-1802. Took about 1/2 hour (I’ve never made any electronic device before). Seems to work great. Perfect problem solver not only for my ipod but also my battery hog PPC 6700. Gracias gentlemen.

  23. Hey guys, I just purchased a 60gb ipod video 5g and was wondering how well this tutorial applies to the new ipod. I hope it’s similar since the 5g charges via usb and I figure I can just get the lm7805 regulator and rig it up with 2 9vs but I wanted some input beforehand to make sure that this hack is safe for the new ipod. Also, I do you guys think I should get a switching regulator or jst stick with the lm7805 and an altoids case? I’m wondering if the switching regulator will really save me that much battery life.

  24. #232
    I’m in the same spot as you are. I set everything up the same, but also added an external jack to plug in a ac to dc adapter thingy or a car charger. I checked the connections,etc, and it says its 5 volts on the 9volt battery or the jack. What I can’t figure out is why its not charging (well it may be, but the annimation isnt on) and wondered if i had to short those pins. any ideas guys?

  25. hi,
    i would like to use a wall wart in the above mentioned setup. im using an old cell phone charger. My worry is that its output is 5.7v 800mA. Will it work with this setup or do i need more voltage? Also, the current is rather high at 800mA. Wont this destroy the shuffle??

  26. Great device, I need something like this for a road angel (speed camera detector) so I dont have to use the in-car charger. Is it possible to buy this device? Havent seen anyone who sells it

  27. Req#232 I have a 30G Video Ipod. I just did it. It works fine, except I dont know if its charging the iPod since when I turn it off, the charging sign isnt showing. It works for Mini and Nano. Is it possible that it needs more voltage to charge the 5g iPod, and if so, how much more voltage does it need?

  28. regarding 101-102 post. as mentioned by marc, can we use this battery pack to power devise that doesnt come with a battery? i bought aivx ( few months ago, and i hv to say it is a great product. it will be much more beter if i cud make it completely portable. the devise hv an 5v dc power inlet. it is also mentioned there 1.5A, if any1 knows wut tat means…

    it will be great if sum1 can help me wit diz.. been going around months on the net looking for a sutaible battery pack..


  29. … where do you buy a lm7805? the explanation was clear, but i didn’t quite get the “you local hacker store part”… I know you can get it online, but where else do they sell these things?

  30. I checked the site for specs on the 7805 and english is the only supported language. I’m thinking what would the other languages voltages be like:

    Irish – all over the place
    French – 12 volts because thats how they say it is.
    Italian – +5 volts until their leader gets caught then it goes upside down and becomes -5v
    Russian – it eventually gets to 5 volts and drops down to 0 for no reason.
    American – stays at zero because the voltage can’t figure out how to travel because it went to public school

  31. Does the iPod shuffle trick have to be used with the 30 gb Ipod Video?? just wondering because I did this, but when I plug in my ipod, nothing happens, but when I use a multimeter to check the voltages, I get a perfect 5 volts. Any help would be nice.

  32. Just finished my usb battery. Used to charge my ipod nano. i simply used 4 NiCd or NiMh cells (AA) and connected it straight to the USB port. the voltage reading was about 5.4V, and this is just a bit above the official USB tolerance of 4.75V – 5.25V, and my nano had no problem with it. you dont need any fancy electronics, or connecting 9V and 1.5V cells together, simply two wires. the usb device can handle a much wider tolerance than the official values. hell, the ipod can handle 12V with firewire, minimum, and that can increase up to 20V or 30V.

  33. I’m pretty sure it won’t work for an ipod video. My old belkin 12V-> USB adapter for my cell phone works for my Mini, but not my 30GB ipod video. The specs are 5V, 500 mA, which matches USB high power. I haven’t tried modding it using the shuffle trick.

    I suspect it may have something to do with USB high power requirements — which require a device to negotiate before switching to high power mode. Perhaps the video and shuffle are in this category?

    In any case, it IS possible, with the right specs. Note that the apple USB charger output specs are 12 V / 1A, and is compatible with all ipods, including video and shuffle (so either the “shuffle trick” is used, or the higher voltage overrides any logic that waits to charge until the bus controller).

  34. you do not need regulators or anything. simply get 4 NiCds or NiMh, which should give you a voltage of about 5.4. to 5.6V. then connect the wires to your usb port and done. i made mine out of a battery holder, two wires, a piece of solder, and a usb port. thats all there is. and my ipod works, and charges faster than it did on the computer

    Keep it simple stupid

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