How to Protect Any 18650 Cell





Introduction: How to Protect Any 18650 Cell

In this instructable I'll show you a very useful life hack that is used to protect any 18650 cell. You can make it only with an old cell phone battery and with some wires. The Lithium ion batteries that are used in phones have a build in protection circuit, that automatically turns off if the voltage of the cell is smaller than 3 volts. This will save the battery from overdischarging. We can use this protection circuit for any Lithium ion cell, like a 18650. The salvaged (from laptop) and the cheap 18650s haven't a protection circuit.

Now go salvage the parts!

Step 1: Tools and Parts

*soldering iron
*wire cutter

*18650 or any Lithium ion cell that you want to protect
*some wires
*an old phone battery

Step 2: Prepare and Salvage the Circuit

Get your cutting tool then try to open up the battery. Be careful, do not short the circuit, may cause fire! Cut the input wires of the circuit then check which is the positive and the negative input. You'll see there three output pins. One is the signal pin and the others are the negaitve and the positive output. You can see the + and - marks on the battery, these marks show you which are the output pins. If you salvaged the circuit go solder to the 18650.

Step 3: Prepare Wires

Prepare four pieces of copper wire.

Step 4: Heat Up Your Soldering Iron!

Easily solder together the circuit and the battery using some wires. Be careful with the polarity and do not short the battery. Do not leave your soldering iron on the battery for much time.

Step 5: Testing

Get your multimeter and test the output voltage. If it,s Ok you're done. You can use now for any project because the cell is protected. That's all.

Hope you liked, write your opinion or other ideas! Good bye!



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    A normal mobile lithium battery protection circuit will not hold any longer to a 6000mah 18650 battery..........the chip don't allow that much current through it(the circuit will assume it as short circuit and cuts the supply)
    This can be solved by using 4 or more circuits in one cell........that is connected parallel to the battery.......and the output of each circuit can be merged together and can discharge with higher current...
    Sorry for my poor English.......hope it helps!

    there is no 6000mAh 18650 in the world!!
    most capacity for 18650 single cell is 3500mAh!

    i said there is no "18650" cell with 6000mah capacity.

    other size of lithium ion batteries could be in many other capacities.

    but 18650 cylindrical cell can not be more than 3500mAh

    .and there is a better way to protect a lithium 18650 or a lithium polymer battery using BMS (Battery management circuit)

    ..a BMS can protect the battery from over discharge current protection ,under voltage protection ,over voltage protection...BMS are avaliable as 1s,2s,3s and 4s at a reasonable cost. BMS can have a discharge rate of 10A or higher...Also a normal BMS is only used to protect a cell ,they cant be used to charge the cells ..they may charge but the charge current will be low as below 1amp at 3.6v nearly...u still need a battery balancer to charge multiple cell...but there are BMS with balancing but i have'nt worked with it....

    here's a link for BMS with balance charging

    they cost a bit higher compared to normal BMS

    And i cant seem to edit my previous comment so i'll just post this here..


    It is one of the best ideas on this site I have come across so far... I made it, but it does not seem to protect against anything. Charging current is not limited anywhere below 2A, and cell discharged below 2.6V. I salvaged from an old Samsung battery. I wonder what the circuit does, if not limiting charging current, and cutting off below a save voltage (2.75V lowest?)... Any idea?

    Can I use also the nokia charger, to charge the 18650 with the nokia circuit ?



    Very good to know, thanks. I'm assuming the protection circuit can only handle fairly low currents?

    No, the circuit don't changes or regulate the current.