Introduction: Cell Phone Charger From an Old 9V Battery

Picture of Cell Phone Charger From an Old 9V Battery

This instructable shows how it's possible to make one 5V usb charger from an old 9V battery, useful to charge cellphone's batterys.

The charger in the picture it's already working - it already charged my cellphone last night. But it still needs to be closed inside some case, that should be the 9v battery case kept from it's disassembling process.

However, here goes the instructions, with the electronic scheme included...

Step 1: Materials

Picture of Materials

The picture shows the components needed to assemble the charger, including one empty case from an old toothpaste, that can be useful to put the charger inside in the future, in an updated step...

And the list of components and materials is:
1 old 9v battery
1 USB port type A (female)
1 Regulator 7805
1 green LED
3 resistors 220R
1 empty case (optional)

Step 2: Schematic

Picture of Schematic

In the computer, using any electronic circuit maker, can be made one scheme like the one in the picture, where I've added a diagram of the pinout of the regulator 7805 and of the USB port.

Step 3: Solder the Components

Picture of Solder the Components

After the disassemble the old battery, the base with the connectors it's useful to solder the components on, starting with the Ground pin of 7805 (pin 2), soldering it directly to the negative pole.

Pins 1 and 3 must be softly lifted up, in order to solder the other components, according with the scheme of the previous step.

One resistor is connectd in the positive pole with a minor size than the base, in order to connect to the Anode of the LED, making a series from the positive 9V pole to Pin 1 of the Regulator.

Pin 3 of the regulator (output 5V) is then connected directly to pin 1 of the USB port, soldering a wire.

The Data pins of the USB connector are connected with 2 pull-up resistors to the pin 3 of the regulator

To finish, pin 4 of the USB port it's connected with a wire to the negative pole of the battery, where it's already connected pin 2 of the regulator.

The result must be like shows the picture, where we can see the charger charging the battery of my mobile and we can read in portuguese: "Bateria está sendo carregada" - Battery is being charged... ;)

Step 4: Final Product

Picture of Final Product

And the final product must be like it's shown in the picture! Now I have one mini-charger, handy to have in the pocket with a battery, for the urgencies. ;)


AbhiR8 (author)2017-04-01

What if i use 2 sony rechargeable 2700 mah Battery replace to 9v battery and connect to solar plate?

is this possible??

i think i can use circuit of Small car mobile charger

ping me about it

MobiOnC (author)2017-01-12

You can now charge your laptop or mobile online. No charger required. Check out the Online Charger website -

S.m.V (author)2016-12-21

can i use potentiometer to maintain 5v supply

solferntc (author)2016-10-12

And if i do that but with a 10.8V DC laptop battery? Would it charge the cell phone faster and last longer?

jaimealmeida (author)solferntc2016-10-19

Of course. A DC laptop battery has certainly more quantity of electrical charge than a normal 6LR61 battery and it has also the advantage to be rechargeable.

ishaans9 (author)2016-06-12

i have 2500 mah battery in my phn what if i made this charger for how much time the battery can charge my phn and how many times a 9v battery can charge my phn

jaimealmeida (author)ishaans92016-06-12

First you must know that this is not intended to charge the phone - it's only for urgencys... The 9V battery supplies about 25mA, which means that it would need about 100h to charge the battery of the phone, but what happen's in the reality is that the 9V battery will discharge very quick because of the inner resitance of the cellphone is low.

ishaans9 (author)2016-06-12

i have 2500 mah battery in my phn what if i made this charger for how much time the battery can charge my phn and how many times a 9v battery can charge my phn

Gomi no Sensei (author)2015-11-30

Most smart phone batteries are 1500-3300mah.

A 9V battery has 50-400mah and at 500mw load has less than 300mah capacity.

You're also losing 30% of that 300mah thru the 7805 as heat.

Just exactly HOW much does this remaining 210mah charge your phone ???

Ref :

ajithgopi (author)2015-10-20

Why is data needed for charging?

daniellong2 (author)2015-06-22

this is probably not going to charge the battery, but it will work as an external battery (the phone uses the 5v input instead of the internal battery) because I already tested it and the only thing that happened is that the battery level was always the same until the 9v got depleted

hyderabad2001 (author)2015-05-29

Thanks for helping me out

hyderabad2001 (author)2015-05-28

hey guys can u tell pls tell me that where can we usuallyfind a 5v regulator at home

at home you can find 5v regulator at every Power station of many devices, like PC's, DVD reader/writer, etc. Every equipment that needs 5V to work, uses a regulator like the 7805 or other to assure the right voltage.

But, if you're looking to scavenge an old equipment to get one 7805, Forget it, because it already has many hours of work and it's not the same as one brand new for sure, that is very cheap...

copeland.royall (author)2014-08-05

I can't get mine to work even after spending ages studying the schematic

well removing the led seemed to work but I'm sure it was in the right way around before

It really works, but you have to be carefull, in a way to don't let any pin to touch each other, avoiding any short-circuit between all the components in the circuit. It's the most dificult in this charger is to keep all the parts isolated...

efahrenholz (author)2014-03-28

This will charge the battery. It will also severely shorten the life of any 9v you use because its a linear regulator. It turns those extra volts to heat. the higher over 5v you go, the hotter its going to get. You can buy cheap switch mode regulators that will buck/boost the input power. Then you can get more life from the input battery in emergencies.

jaimealmeida (author)efahrenholz2014-03-29

Thank you for your suggestion, but this is supposed to be an easy way to construct one cheap mini charger, that has many alternative possible solutions to be constructed and updated, like the way you suggest. I just didn't even think about the life of the battery, because it's just another old battery that I've made good use from scrap...

peabody1929 (author)2014-03-26

The green LED will limit the charging current to about 30 milliamps.

jaimealmeida (author)peabody19292014-03-27

The current aplied in the pin 1, where is connected the green LED, will be I = V/R = 9/220 = 40,9mA, which is a good Intensity value admitted by the circuit.

You must consider that this is just an handy charger to disentangle any situation, therefore the output power of this charger it's lower than the normal chargers, which makes the charging process to be very slow...

jbrown120 (author)2014-03-26

Do you know the amp/hr of the charger?

captainchaoss (author)2014-03-26

heres where i betray a complete ignorance of electronics: so if i make this, i can fully charge my cell phone from a 9 volt battery in a pinch ?

Penolopy Bulnick (author)2014-03-26

Very handy!

About This Instructable




Bio: I am a portuguese Engineer of Electronics and Telecomunications who loves inovations...
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