DIY Powerbank With Refurbished 18650 Lithium Cells

I've recently found a lot of dead drill batteries at my workplace, and asked for permission to take them. so i now had a lot of "dead" drill batteries with 18650 lithium cells in it, that i wanted to make into a powerbank.

I've used following

1. Tools
2. A soldering iron
3. My 3D printer (I've got an old ender 3, but pretty much every 3dprinter should be able to do it)
4. Wire stripper
5. A spotwelder (you could also use you soldering iron to connect the lithium cells, but you run the risk of losing some capacity if you heat it up for to long)
6. Materials
7. 4 Lithium cells (i got mine from the old batteries) - Free
8. A powerbank module (i had an old powerbank laying around with a depleted battery, so i used that. But you should be able to source a board for around 2 - 3 euro) - Free or 2-3 euro
9. 1 roll of electrical tape - 0,5 euro
10. 1 Tp4056 module - 0,3 euro

When you're working with lithium cells should you always keep safety in mind, especially when you are working with refurbished cells. I would always make sure to do it near an open window, wearing a mask, wearing gloves and, having a metal bucket you can put the cells in, if they suddenly should catch fire.

the liquids in lithium ion cells isn't a joke and can really mess you up if inhaled, so make sure to always take safety precautions.

The first thing we'll need to do is disassembling the battery. this is pretty much the most dangerous part. we'll start by unscrewing the screws and taking the plastic cover of. You should then be able to see the cells and circuit board, cut off the protection board, i just used a scissor, BUT BE AWARE NOT TO SHORT ANYTHING, it could end really bad.

the last thing to do is just to separate the cell from each other, you should be able to just take a wire cutter and just pull the nickel strips off. Again be aware to not short or puncture the batteries, but if you do make sure that no liquid has spilled out, if there's no leak and the batteries doesn't heat up by more than 5 degrees Celsius are you fine, but if its heating up or leaking then put it in the bucket and take the bucket outside. No need to risk your life.

I'm using a cheap 18650 battery tester as seen in the picture to measure capacity an the internal resistance. But i need to determine if the battery can be recharged before i put it in the battery tester. i determine it by firstly measuring the voltage of the cell, i would discard every cell that is below 1,5 volt.

i will then measure the capacity of all the batteries that's left, i just need 4 with around the same IR (Internal Resistance) an capacity, i found 4 batteries with around 2040 mAh and an average of 50 milliohm.

I started by using a flat head screwdriver to open up the body of the old powerbank. i then took out the old dead battery out and used my soldering iron to remove the USB board from it.

i then used my hot air gun to get the micro USB port of because i want to charge the battery pack with an external TP4056 board as shown in the schematic in the introduction.

ive used fusion 360 to design the powerbanks part, the powerbank is made from five pieces

1. The battery compartment, it's just a square with a couple of fillets and an indent for a plate to be glued on.

1. Battery details, its the electrical characteristics of the battery. made to be glued on the battery compartment. Its just a 20 x 40 mm plate that's 0,5 mm heigh and some text on, so its easy to recreate with your own details.

1. The middle plate, is just a simple separation from the battery to the modules with 2 holes to run some wires to the battery. looks great if you give it another color than the other pieces.

1. The top, made with holes for the modules.

You need to be careful when assembling the battery. before you spot weld (or solder) the nickel on the 18650 cells should you make sure all the cells are placed the right way, so the positive on top and the negatives on the bottom.

i cut the pieces to size before i began spot welding them to make the process faster, but it isnt nessecary, i made 2 longer pieces to solder a wire on. i them put fish paper on both terminals and covered the whole pack in electrical tape, just to isolate it and avoid any accidental short circuit.

So i began by putting the battery in the case an toping it of with the middle part and running the wires through it. I also placed the information plate onto the battery compartment by just using hot glue.

I then took the top part and placed the 2 modules on it. I placed an USB cable on the powerbank module an just filled it with hot glue, the USB cable is to avoid glue getting into the connector. I then connected the wires and used a 3D pen to attach the pieces together. And that was all, the powerbank is now done.

That was all, now you have a powerbank thank can charge the average phone almost 1,5 times. have fun with it.