Introduction: Portable Phone Charger

Picture of Portable Phone Charger

My wife recently got the LG Lucid. Much to our dismay, the battery life was gone by about 3-4 in the afternoon from a full charge that morning. She loves the phone, however, so I thought a portable battery charger might be a good solution just in case she's in a store or somewhere without a car/wall charger. This is what I came up with - my 1st instructable! 

There are several of these around the net, but most people use an altoids container, a 5v voltage regulator and a 9v battery. I built one of these and it sucked. Because 9v bats only hold around 450mah at best, it charged the phone about 5%, which rendered it useless.  It also uses a female USB plug, which means you have to carry around a USB cord with you, which is extra hassle. I wanted to create something that used common easy to find parts, and was cheap to build. This whole project costs around $4 to build, and it charges the phone anywhere from 25-40% depending on the type of batteries you use.  

Step 1: Parts List

Picture of Parts List


1x Battery box  - $1.99 (I saw it at another Radio Shack for $2.29, but my local one had it for 1.99)
4x AA batteries - $.50 (I went to the dollar store and bought this 8 pack for $1)
Cell phone cord  $1.50 (I found one cheap on Amazon, but make sure you get the one that fits your phone)
1A diode (these are very cheap if you buy them in bulk - probably in the 10 cent range). 

Soldering iron / solder
Heat shrink tubing, or you could use electrical tape I suppose

Step 2:

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1st, cut the cord, leaving about 3-4 inches from the part that attaches to the phone. You need to strip the cord back and you'll notice some insulation, probably some foil, and 4 wires: red (+), black (-), and green and white wires (data). Cut it so that you leave just the red and black wires remaining. The green and white wires are only for transferring data, which you will not be doing. Which leads to an interesting point - this charger cannot be used for an iphone because Apple created phones that draw current from the data cables - I think around 2v each. Even though you could make something to charge an iphone, it would require resistors to drop the voltage on these 2 cables. I don't have an iphone, so I didn't care to do this. 

Cut the black and red wires coming from the battery box leaving about 1.5 inches left. 

Take your diode and cut it leaving about 1/2 - 3/4 inch left on each side. (You'll notice that this is a 3A diode and I mentioned before that you'll need a 1A diode. I didn't have a 1A diode and didn't want to buy one, so I used this 3A one. But 1A is all you need. Wall chargers allow 1A.) 

Step 3:

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Before you solder the wires, you need to slip on your heat shrink tubing, and smaller one that goes on the black wire, push it towards the battery box so that it doesn't come in contact with any heat while you're soldering, otherwise it'll shrink and you'll have to cut it off and put on another. Now get a larger one and put it on both wires, but push this one toward the plug end. This one will cover both wires, the other one covers just the black one. Obviously the 2 wires cannot touch each other. The larger heat shrink tube is large enough to cover the soldered area and around the diameter of the diode, but not big enough to slip on and off the end of the cable. 

* Heat shrink tubing is cheap, and if you're a tinkerer, grab yourself a box of them, you'll use them all the time. But if you don't have any, all this can be accomplished with electrical tape, it just won't look as nice. 

Solder the black to black 1st, then wait till if fully cools before slipping the tube over the connection. Once on, heat it to shrink it, and move to the red. This is where the diode has to go. Make sure the diode is soldered in the right direction, otherwise current cannot pass beyond this point. The stripe on the diode represents the cathode side (negative) and it leads away from incoming current. So this side (see the picture) will be on the opposite side of the batteries, or the side that is closest to the phone plug. The solder the red wire coming from the battery box to the side of the diode that doesn't have the stripe (the anode). 

Wait until fully cooled and then slide the larger tube that you had already slipped on before you soldered the diode on. Heat to shrink.  

Step 4:

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At this point, you could leave it. I decided to put one more piece of extra large heat shrink tubing on the connection, just to reinforce it. The cool thing about this battery box is that is has an on/off switch.

Put in your batteries, close the lid and charge away.

* This box takes 4 AA batteries and if you know anything about batteries, you know that non-rechargeable batteries carry a voltage of around 1.5 volts. Most rechargeable AA batteries carry a voltage around 1.2-1.3 volts. We need at least 5 volts here to charge a phone. Your USB cord, whether plugged into a wall jack or computer, will allow around 5v to pass because that is the minimum voltage needed to charge a 3.5-3.7v phone battery. So 4 rechargeable batteries would give you about 4.8v, and even though technically this would momentarily charge a 3.7v battery, especially if it's a dead battery, it will take a long time to do so and would probably only give you about a 5% charge. 4 regular batteries gives you 6v and will not only charge the phone more, but also much more quickly. Since these are cheap at the $ store, this is what I used. With the cheap ones I get about 25-30% charge from a dead battery. If I put in Duracell bats, it will give be around 40-50% charge, but this is an expensive way to go. 

Step 5:

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And you're done. As you can see from the picture, it is plugged in and is charging as indicated by the orange LED at the top. Look at the phone and you can see the battery charging symbol next to the time at the top right. 

And that's it. Remember to turn the switch on!!  =)  Good luck. 


Vitor Shaft made it! (author)2017-01-21

In my case it was not needed to be connected to a transistor or even a diode to work

AdeelA5 (author)2015-05-02

How would we recharge the battery,,,,,,, to reuse or recharge the phone....???

AntonioQ1 (author)AdeelA52015-10-23

If you replace those with rechargeable batteries it should work the same and you can recharge the batteries with a battery charger (10 bucks at radioshack)

haval101 (author)AdeelA52015-08-29

probably reloading the batteries...

taneshg (author)2015-10-22

I made it recently but the diode is heating up very much! Please help!!

AntonioQ1 (author)taneshg2015-10-23

That happened to be too, but I fixed it by attaching a very small heatsink to it (about $5 at radioshack or 99¢ online) with some thermal glue and it stopped heating up.

sourabhmech (author)2015-09-16


what is happend when we increase the voltage of the battery which we use

DarrenTatch (author)2015-03-30

I recomend iPowerBuddy which i got from amazon ,dual port. 10000mah ,flashlight ,lightweight brilliant , think they had coupons also listed on their facebook

TanmayNaik283 (author)2015-02-24

Would it work for a Li-ion battery?

And is heat shrink tubing absolutely necessary?

thenicedoug (author)2015-02-12

Don't buy anything from Amazon unless you use AMON DEAL FINDER (just google it). They have a yellow widget on their website that finds all of the different merchants who sell the same products and spits out the discounts that you're looking for. This tool really puts you at an advantage for saving money on Amazon. This charger was about 60% off from one vendor and it's been awesome since I bought it. We use that widget before buying anything on Amazon now. Just amazing.

redeagle20 (author)2015-01-08

can i add capacitor?

donjusi17 (author)2015-01-01

After this debate, what kind of Diode should I use? We have the same bat.

ecoss9 (author)2014-09-17

disculpa las pilas se pueden recargar y de que manera??

Alec Adams (author)2013-08-25

this actually works!! but soldering sucks!!

its_khal (author)2013-05-19

Nice one there TylerPA. But how long can it charge an Android phone? 4AAs? I'm thinking it wld just die in minutes. Pls, i'm a heavy phone user. I have a ups battery 12V 9amp i wish to use to charge my phone. Could you help with the circuits to go with it?

!OpTIMisTiC! (author)2013-01-19

Do we have to connect red wires with diode???? and not the black ones.

Wareneutron (author)2013-01-03

it will damage your device...
you don't know?

Wareneutron (author)2013-01-03

i have own version of your phone charger but put a little interactive LED indicators!

Wareneutron (author)2013-01-03

wow what the project do you have?

+_mElChIzEdEk_+ (author)2012-08-09

how will i connect the diode?

warmflatsprite (author)2012-07-05

You're really supplying about 5.4V to the phone, assuming there's a 0.6V diode drop. Either way, the statement that 6V will charge your phone more and more quickly is a bit misleading.

USB is standardized to 5V, and as such, I would strongly recommend against supplying anything but 5V to the USB circuit. You can probably get away with +1V or +2V over, and you're right that this will, depending on the regulation in the charging circuitry, charge the battery faster, but it also could cause much higher heat dissipation and stress your battery cell. Alternatively, if you don't get away with it, you'll fry the charging circuitry and need to replace your phone.

TylerPA (author)warmflatsprite2012-07-05

Incorrect. The voltage drop is only about .3V, I tested it before the diode and it was at 6.2 with fresh AA's, and 5.9V after. This is well within the manufacturers recommended voltage supply (4.9-6.2V) to the phone, which was double checked before I made this instructable.

Furthermore, I've used this charger many times over a span of about a year and a half and the battery life is the same as it was on day one, nor has it "fried" any circuitry.

Furthermore, it's common knowledge that batteries need a voltage rated at 1.5x (+/- 10%) the batterys' capacity voltage to effective charge it. On a standard 3.7V cell phone bat, this would place an ideal voltage charge of 5.55V, +10% would be a max of 6.105V, and a minimum of 4.995V which is almost identical to the manufacturers recommendations.

skrubol (author)TylerPA2012-07-13

Be careful throwing around 'common knowledge' like this..
For NiCad and NiMH that rule of thumb may work, but it does not hold true for Lithium Ion's. An unprotected lithium ion cell could catch fire or explode if charged to 5v. It would definitely vent and be ruined. Lithium Ion's max charge voltage is 4.2v.

Cell phones and most other devices with li-ion's built in have charger circuitry built in to the device. Typically this charging circuit is built around the USB spec for input voltage/current. USB VBus spec is 5v +/- 5% (or 4.75-5.25v) Anything about 5.25v could possibly damage connected devices (though I think pretty much any USB device is tolerant of 5.5v.)
Furthermore, fresh alkaline batteries with no load will put out 1.58v each, so your starting voltage will be 6.34v.

warmflatsprite (author)skrubol2012-07-13

To further skrubol's comment, the term "charging voltage" doesn't really apply to Li-Ion and Li-Poly batteries, as there are multiple charge phases - some of which are constant current rather than constant voltage. The voltage that you're feeding your phone from your charger is the input voltage to your phone's internal charge circuit.

My original point is that while it may be safe to say that this design works for your individual phone, you have no way of saying that it works with all Li-Poly and Li-Ion charge circuits found in phones today, and as such it represents a hazard to novice would-be builders.

maxhuey (author)2012-07-05

".....the battery life was gone by about 3-4 in the afternoon from a full charge that morning"

Unless she talk for 8 hour straight, that phone should give you several days of use. There are a few things you need to do...

- while the phone is new, charge it up to full and use it until the phone is almost dead. do this for the first 3 charges.

- Kill all the apps running in the background, including default programs like life wall paper etc. Go to settings-application-running services to see which things you do not need running. Kill them.

- There are battery booster apps that will do this for you and they are free...

My LG goes for more than 2 days with just below average use and 1.5 days with lots of talking, text and net surfing. If you do the above and still not getting good battery life, then the battery is defective and warranty willl get you a new one.

lovethebackwoods (author)maxhuey2012-07-06

Maxhuey, I have a Wal*Mart LG phone of some type - LG800GHL. I have not found anyone among my tech-savvy friends who can figure out how to disable the browser, the set world clock locations, or the keyboard tones. I would like to be able to turn it on and off or give certain commands without all the beeping and tone series. There are times I apparently pick it up wrong or something and even with the lock on, I suddenly find the browser eating up my airtime. I never browse! Is there a way to get rid of it or do I need to just shoot my phone?

maxhuey (author)lovethebackwoods2012-07-07

standard lg process, menu, settings, application, then go to manage or running service to look for things you want to do. other function are in the settings sub menu. your phone company should be able to help you with stopping you browser from running by itself as this has been a real problem for many people, and the phone company love it too. unfortunately CSR arehard to get hold of, sometime waiting for hours to talk to one. If you were in my town(vancouver), it would be much easier for me to uust do it for you or, show you how to do it. cheers, max

maxhuey (author)maxhuey2012-07-07

Sorry I was using my phone to type so lots of spell mistakes....
I remember when my in-law's got the iPhone from Fido, he got billed with over $1,000 air time every month because his browser was turning on by itself every morning, showing him the stock market. Not knowing what to do, he simple hit a couple keys to turn the screen off (browser still running). After getting more than a couple $1,000 bills, and the battery drying up in less than 24 hours, we called Fido to have them block the data browser, but occasionally, the browser still popped up. In the end we decided to use a software, available free in the internet ( to block the data completely. That was a couple of years ago and since the phone companies got lots of complaint, they decided to do away with pre-programming the handset with auto browser. You case might be different but still you should call your phone company to complain and ask for instructions to block data browser. Hope this help. max

wmiller4 (author)2012-07-05

I build one like this to power an mp3 player via USB while traveling long hours on greyhound - mine uses 4 D batteries and lasts about 200 hrs .

TylerPA (author)wmiller42012-07-06

Yes, that would be awesome - D bats hold the same voltage as AA bats, so input voltage would be the same, but you're right, the amp hours would be tremendously greater. My goal was to make something compact so that she could put it in her purse. 4 D bats would charge the heck out of something, but would be big and bulky.

wmiller4 (author)TylerPA2012-07-06

you do have a point about the portability - I guess if space was no consideration we could get a motorcycle battery and build a big frankencharger - lol

e5frog (author)2012-07-05

Nice and simple, is that voltage recommendation valid for all USB-charging phones?

Cord seems to get a bit rigid with all shrink tubing.

I'm amazed over the super cheap things you seem to have over there, only $1.99 for a battery box with an on/off button...

There are 2AA chargers that also works for iPhone for just $0.99 including shipping on e-bay. Perhaps getting one of those, grab the circuit and put a larger bank of batteries in could be something...

TylerPA (author)e5frog2012-07-06

Depends on what battery you have and what it's rated for. My phone bat was 3.7v and manufacturers suggest supply voltage was 4.9-6.2. So anywhere in that range would effectively charge the battery according to them.

Yes, the cord is a bit rigid, but it doesn't bother me, it just butts up against the bat box when not in use.

ARJOON (author)2012-07-05

bit too dangerous to try on my phone, no regulation or constant current etc....

tutdude98 (author)2012-07-02

after the diode voltage should be about 5.1 - 5.2 volts??

Orngrimm (author)tutdude982012-07-02

It depends on the diode. A normal Silizium-Diode has 0.6-0.7V flow-voltage.
A Shottky-Diode has 0.2V.
So you have max 4x1.5V = 6V before the diode.
That makes 6V - 0.6V = 5.4V (for silizium) and 6V - 0.2V = 5.8V for a Shottky-Diode.

If you want to be sure you dont grill your device with a voltage too high, you can add a regulator (While ditching the Diode all together.
Simple but wastes energy: LM7805 (>13% loss)
Complex and more efficient: Omit the Diode and go for a Buck-down DC/DC-converter like (around 5% loss)
But to be honest, that would make the project much more complex for every non-technician or -electronician.

TylerPA used the Diode as a simple, yet effective way to reduce the voltage. Call it a poor man's LM7805 :)

tutdude98 (author)Orngrimm2012-07-02

so with this i can charge phone just like using 9v battery and LM7805?

omnibot (author)tutdude982012-07-02

Yep. I made one a while back and it works great. The voltage of 4 fresh alkaline AA batteries is actually about 7 volts and with a 4007 diode it drops to about 5,7 volts. That is really to high but when you put a load on it it drops further down to around 5,5 volts which is within limits of the USB-charging.
4 fresh AA's usually gives a full quick charge and a slow trickle as the overall power drops. I've gone without power for a week on travels with this. Make sure to use a good diode, not a tiny little zener. They get too hot and burn on full charging.

TylerPA (author)omnibot2012-07-02

Yes, thank you. The little Zener diodes will fry. I tried one and it started burning my fingers within a few seconds. Kind of cool, but won't be much use here.

Orngrimm (author)omnibot2012-07-02

A zener-diode is a special diode with specially tailored breakdown-voltage. For normal forward-voltage is around the same as with a normal silicium-diode. See for details.
"zener" does NOT tell about the wattage. The 1N2846 is a zenerdiode and has 50 Watts... ;)

4007 or 1N4007 is the same as every 1N400*. The only difference there is the reverse-voltage. And the weakest is the 1N4001 with 35V RMS. So more than enough. Go and choose whatever 4001-4007 you find.
See for a listing of 1N4001-EM518 while the EM* are a continuation of the 1N4007-13.

And to be clear: 4007 is NOT a description of the diodes power dissipation-capabilities. It is simply a Model-name (1N400*) for a common diode with different (*1-7) reversevoltages. However you are right: The 1N4007 can dissipate 2.5W of power. But only if not covered with shrinktubes like you do :) So the power may be around 1-1.5W i think & guess.

The absolute normal standard-diode is the 1N4148 and has 500mW of powerdissipation max. THAT would be not enough for sure if you shinktube it and run a full highpower-charge.

I hope to have brought some clarity to the world of diodes. ;)
Yours, Orngrimm
Electronics Engineer, Dipl HF electrotechnics

TylerPA (author)Orngrimm2012-07-02

Yes, you are correct, it's a "poor man's" charger, which was my goal. There are far more advanced ways of building a cell phone charger, but it ups the cost as well.

Also, 6v is certainly not high enough to "grill" the device. And yes, the diode does drop the voltage just slightly.

TylerPA (author)tutdude982012-07-02

No, with fresh AA's, it would be closer to 6 to 6.2v, but as commented below, the diode as a tiny drop in voltage, so my output was around 5.9v. This is certainly within the range of "ok" regarding cell phone charging.

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