Introduction: Reuse Old Phone Batteries As a Powerbank (earth Day Part 1)

Picture of Reuse Old Phone Batteries As a Powerbank (earth Day Part 1)

I guess you probably also belong to the majority of the worlds population that owns a smartphone and you probably had more than one during the past few years of smartphone evolution.

With them, come used lithium ion batteries that you can not just keep on using inside your new phone.
So you are stuck with useless batteries. I have 3 of them and I did not change my phone because the batteries were dead.

They did not get hot or start to swell so they are still able to power devices. The average lithium battery has 80% of it's original capacity left after 2 years of usage, which is the period in which I usually buy a new smartphone (not because of the better specs but because of major hardware issues).
And think about the energy that went into extracting the raw materials, producing the battery and shipping it.
Considering all that it would be a real shame to just let them slowly die or throw them away.
In this instructable and in my video, I want to show you how to build a device that enables you to repurpose your old phone batteries as a powerbank for newer devices.

Step 1: Materials

Picture of Materials

Let's start with what you will need for to build your own recycled powerbank.
The materials are:


  • a switch

The required working equipment consists of

  • a knife
  • a pair of pliers and a wire cutter
  • a soldering ion
  • a hot glue gun


  • a drill or dremel tool

Step 2: How Do the Boards Work?

Picture of How Do the Boards Work?

Let's take a look at the lithium ion charging and protection board. It has three important functions.
The first is charging. Lithium ion cells have a certain charging pattern. When they are nearly full, their current consumption drops. The board will recognize that and stop charging as soon as the cell voltage reaches 4.2V.
On it's output the board features a protective circuit consisting of an over current and an under voltage protection. Such a protective circuit is already integrated in modern phone batteries and therefore not necessary but it will allow you to use unprotected cells like you would find them in old laptop batteries as well. The charging current of the board can be adjusted through a resistor. It should be somewhere between 30 to 50% of your battery's capacity.

The DC converter takes the dc voltage from the battery and turns it into a square wave that is send through a little coil. Through inductive processes a higher voltage is achieved. It is converted back to DC and can be used to power 5V devices.

Now you know what you are dealing with, time to start making .

Step 3: Planning

Picture of Planning

Before you begin to make the enclosure, take your measurements and make a plan.
My device is supposed to be held in place by the paper clamp, so it will be bolted to the enclosure. The two pcbs will sit on top of each other with the in- and output at the top and the battery pins at the bottom.
Some phone batteries tend to have a different polarity than others, so the device needs pins with interchangable polarity. To add this type of functionality I used the arduino pins and slots.
A piece of three slots with the middle metal connector ripped out and the 2 outer ones bend to the side can be used as a battery connector.
The counterpart will be a row of 4 pins with positive wires connected to the outer two and a negative wire connected to the two in the middle.
This way the polarity can be changed by plugging the battery connector in on either the right or the left side.

Step 4: Make the Enclosure Parts

Picture of Make the Enclosure Parts

Time to make the enclosure. For this you use your measuring tool to find the right with and use the knife to scratch the surface about ten times. Then you can keep in without the measuring tool and more force. When you are about half way through, place your pliers next to the cut and bend the materieal until it breaks.

When all the parts are cut out sand and test fit them. Fix them on a stable surface and start making the holes for screws, switches, inputs, outputs and pins using a dremel tool.

Step 5: Solder the Boards Together

Picture of Solder the Boards Together

Before you can assemble the parts you need to wire the boards. The shematic shows how they have to be connected. The small switch turns the dc converter on and off.

Step 6: Put the Pieces Together

Picture of Put the Pieces Together

Use hot glue to stick the pcb's together and to stick the onto one if the plastic pieces. Glue all the pieces in place and screw the clamp on.
Plug tha battery pins in and test it.
If it does not work, try plugging the charging cord in.

Step 7: Use It!

Picture of Use It!

Now you have a new purpose for your old batteries.
My enclosure is definitely not the best looking solution but it's nice to show the concept. I bet that you can come up with some much more creative ideas.
In my next instructable and my next video, I will show you another way to recycle those old batteries so follow me to be up to date.


AndrewB581 (author)2017-12-18

Is it necessary to use the switch?

AndrewB581 (author)2017-12-05

Looks great man! I can't wait to try it. I just ordered the parts. Great video and good clear instructions. Thanks

AutobotPrimo (author)2017-04-01

Hey can this not be done with swollen batteries?

AriN14 (author)AutobotPrimo2017-08-17

woah, swolen batteries are a no-go zone. it is probably dangerously close to exploding now. dispose of it at a battery recycling center.

devans27 (author)2016-05-01

Can you stack them in series with same setup? To make it a larger mobile phone bank.

Basement Engineering made it! (author)devans272016-05-02

Connecting them in series to create a higher voltage won't work. You should be able achieve a higher capacitiy by connecting two batteries with their individual charging boards or two whole units with a self made charging cord in parallel as it can be seen in the pictures. I'm not 100% sure if this setups would work so you would have to try it.

Thank you for the info, it is very interesting and intriguing! I did have a question though as I am not the most knowledgable when it comes to electrical engineering and the like. In your diagrams of the multiple LI batteries it looks like the diodes only allow 1 way power usage. If that is correct how do you then charge these? I have 5, 6000mA batteries from my old Samsung that I wanted to string together in a little box and make a large battery pack with a solar recharger on the top for outdoor use but want to make sure I put it together where I can charge each battery on its own from the solar panels but then use them all to make a giant battery pack to recharge my ipad, flashlights, current cell phone or other survival gear.

miraheng (author)2016-06-10

did u use it everyday? :)

My new smartphone has a 3500mah battery which is enough to bring me through one day without recharging so I'm mostly using the device to keep my old batteries in shape. I'm also thinking about a version 2.0 with a proper enclosure for better handling.

meikdre (author)2016-04-26

isn't there already a protection board in these kind of batteries?!

RaymondR6 (author)meikdre2016-05-01

Yes, each commercial battery is a cell with a small PCB on its edge. If you need to use the raw cell, remove the battry covering and see the small PCB attached to the cell electrodes. As a guide for Samsung cells, the external metal body is the positive electrode, while the negative is wired through the PCB. Cut the electrodes carefully and remove the PCB. The new charging board replaces the same protection as the Samsung PCB which can be discarded (it has thermal and overvoltage chips on it).

miraheng (author)RaymondR62016-06-10

did u mean that i can remove from my old smartphone all this components in this project? tq

pierre5325 (author)2016-05-12

Hi Jan, this is a great tutorial. Thanks for sharing it with us. pierre from New Mexico

adillbeck (author)2016-05-02

So I have 4 or 5 batteries from my wife's old phone, all the same, and most relatively fresh. Any reason I couldn't hook them up in parallel to make a massive battery pack with a single charging board?

Or would I need a separate charging board for each battery?

I'd expect a single board to take a lot longer to fully charge 5 batteries.

PhilKE3FL (author)adillbeck2016-05-02

Charging batteries in parallel is not as good as charging them individually. In fact, when I charge my Ni-MH batteries I use chargers that charge each cell individually and not the whole battery pack. I suspect the same reasons would apply for doing it with Li-Ion batts as well. The problem is that not all batteries are created equally and what happens in a pack of batteries is that the strongest batteries cause the charging to stop prematurely, or the weakest cell causes charging to continue to the point where it starts over charging the good batteries. Then if one cell dies completely the pack never stops charging, since it can't reach the shut off voltage, and the other cells are then over charged and then they die as well. That's with Ni-Cds and Ni-MH I have no experience with groups of Li-ion batts but since it is dangerous to over charge a Li-ion batt I would NOT recommend doing this unless you have a microprocessor based charging unit that can shut things down when things are not correct. I don't know of any company making such a Li-ion battery pack charger. Which, doesn't mean there isn't one.

Thank you PhilKE3FL. I could not have said it better myself. Lithium ion batteries behave the same way if they are connected in parallel . The characteristics of the pack are limited by either the weakest or the strongest battery and it it can be dangerous. You should use an individual charging board for each battery.

That makes a lot of sense.

Can they still be wired to discharge in parallel, or should I just drop the whole idea and only use one battery for each powerbank?

If I can still use them in parallel and just get a charging circuit for each battery, I wonder if I can wire the charging boards to the same input power source, and how that would affect the input voltage... I could use a 2A supply and some resisters to get it down to 500mA for each battery... or maybe it doesn't work that way.

You can connect multiple batteries and their individual charging and protection boards as seen in the first picture. If you plug a charging cord into one of the boards micro USB port all of the batteries will be charged at the same time and it will show you which cell is full. Through a few diodes you also get a single output that you can connect to your USB booster. With multiple batteries it should also be possible to use a more powerful booster with an output of 2A.

Using a 2A power supply is also not a problem as the chargers only consume a preset charging current. You can adjust the charging current on each board through a small resistor and it should be set to 30%-50% of the used batteries capacity (less is more in therms of battery life).

Here you can see the resistor and how its resistance effects the charging current.

adillbeck (author)PhilKE3FL2016-05-03

Would something like this work?

Ideally, it would be cool to have one input that feeds 4 of these, one for each battery, and then a single output from the batteries in parallel.

I don't know if this is even possible though, or if I should just drop the whole idea.

Thank you PhilKE3FL. I could not have said it better myself. Lithium ion batteries behave the same way if they are connected in parallel . The characteristics of the pack are limited by either the weakest or the strongest battery and it it can be dangerous. You should use an individual charging board for each battery.

tritian (author)2016-05-03

Well done, excellent idea! One request for next time though, It would be fantastic if you could include links as to where to find the components required. (i.e. the protection board and the DC converter.) It would make life a lot easier and would slingshot your instructable from a 4 star to a 5 star. =D

Thanks for your comments. I will improve my ibles and add a few links soon.

PhilKE3FL (author)2016-05-01

Thanks for the instructable and good work & ideas, however...

"And think about the energy that went into extracting the raw materials, producing the battery and shipping it. Considering all that it would be a real shame to just let them slowly die or throw them away."

I'm just wondering why you aren't using the phones until they die if you're so interested in saving energy and materials?

shortw (author)PhilKE3FL2016-05-01


drofnasnhoj (author)shortw2016-05-02

lol, can you imagine still using a 486DX just cause it still "worked". I'm sure his logic isn't quite sound, but living in the world of old phones can be brutal when trying to run the latest software/games/os.. but then again, I'm picky ;-)

PhilKE3FL (author)drofnasnhoj2016-05-02

I understand, there are many good reasons for upgrading and getting something new or at least newer. My present cell phone is over 4 years old, with the original battery and this one was picked up after the last one died, stopped charging the battery, and after I charged the battery for six months by removing it from the phone and charging it with a Li-Ion battery charger I built. I just got tired of recharging it by having to remove the battery and all.

I still have a windows 97 laptop because it is the only PC I have that can upload/download data to a wide band scanner (radio) I have. The memory program does not work well with newer versions of Windows.

Thanks for your comment.
I think our planet and our world is amazing so we have to do everything to preserve it as it is for the most part, which is impossible but trying is better than doing nothing. Thats why I think about the ecological aspect in most of my decisions and I do only upgrade if major issues occur.
In my first smartphone the calling function did not work anymore even though I tried different things to fix it. The second one was the old smartphone of my sister and is now used by my mother Galaxy SII's are great. I became a heavy user during the past two years and use my smartphone as my main working device. It pretty much replaced my Laptop. This is why my latest upgrade was buying a UMI emax with a 3500mah battery, a fast processor and a huge screen.

Very good led_freak, you should have included that as well so we all knew you were passing them on or they died. That lends far more validity to your saving the battery Instructable.

Osquar (author)2016-04-25

Awesome!! I have a cemetery of still functionable mobile and camera batteries that a few years ago wanted to do something like this with. Couldn't quite make the discussion on here go the way I wanted, some how I made it seem like I wanted to repair them or something.

With other words - Thank you :)

RaymondR6 (author)Osquar2016-05-01

Please be careful which of thos old batteries to use. If the batteyr seems swollen (like a cushion) , discard it because it may have released hydrogen gas inside, and if overheated it can explode.

Osquar (author)RaymondR62016-05-02

That only ever happened to the first powerbank I bought. Had to throw away the bag as well after it exploded. The cell phone batteries are all good quality still. But thanks for the heads up :)

Yonatan24 (author)2016-05-02

600mah output? My phone consumes over an amp while charging...

Can it get burnt out, Or just charge slower this way?

It will simply charge slower than usual. There are also usb step-up converters with an output current of up to 2Amps avalible but such a high current draw would be toxic for the old batteries that you put in there. Always remenber slower charging and discharging increases the life span of your lithium ion batteries. Keeping them somewhere between 30 and 70% of a full charge is also helpful but not that easy to accomplish.

I hope this answered your question:).

JaredS37 (author)2016-05-02

old batteries also make good use as a stabilizer when using solar panels to charge your electronic devices.

WannaDuino made it! (author)2016-05-01

good for earth day probs,but i am also trying a long time to inplement the old batterys look here at my uses. I have a qustion About that, i installed the battery without a battery protection board,because I thought it whas on the unit itself..


WannaDuino (author)WannaDuino2016-05-01

I did not use the blocking diodes on the battery,but only on the solar panels

In my other power bank case I put one on the battery,but that needs to be tested I don't have a conclusion of that yet.

And yes you see I love to make solar power banks.with phone battery's,next I am going to put a 6000 mah lipo battery in it, but that wil need a very big extra panel to charge in the sun.

I really like your solar setups. I also have a few old cells laying around and have been planning on building a small solar tree charger some time ago now and you just brought me back to the idea, thank you for that.

The diode was a pretty stupid mistake of mine. If you installed it like I showed it it disables the charging function which is a little bit counter productive. So the diode is not needed.

It is true that all modern phone batteries have a protective circuit inside them so there is no need to worry about that. The reason my charger features an extra protective circuit is that I also want to use it for unprotected lithium cells.

thank you,Jan.

But what ment whas, the pcb of al power banks. In my eyes the have a protective circuit for battery s. Don't you think to. Or can we say that ,that is an insomtion of me.and must I refer to a data sheet of the board if there is.!

Raphango (author)2016-05-01

Great idea! =D

About This Instructable




Bio: Hi, my name is Jan and I am a maker, I love building and creating things and I am also quite good at repairing stuff ... More »
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