How To Make a DIY Power Bank With Laptop Batteries

Laptop batteries have an average life of between 2-3 years. This lifecycle can be greatly extended if you take care of the battery and never overcharge it. A laptop battery pack consists of 18650 lithium ion cells that are connected in parallel and series circuits for giving the desired voltage. Today most laptops or notebooks use the 4 cell battery which is much lighter as compared to 6 cell batteries. The laptop battery is driven by an intelligent circuit which reports its health and the charge being held by the battery. The circuit notifies the Windows OS whenever the battery gets low or needs replacement. For safety purpose this intelligent circuit discards the entire battery-circuit operation whenever a single cell fails to hold the charge.

However in most cases out of 4 cells, only one gets completely exhausted which is then becomes unable to hold the charge. This situation affects either the battery voltage or charge holding capacity. If the voltage of any cell is affected then the battery will not be able to give any backup. It completely fails and charging does not work. If the charge holding capacity is affected then only the backup is greatly reduced but the individual cell voltage remains unaffected. In this case, you can normally use and charge the battery but don't expect a normal power backup.

So, if your laptop's battery has stopped working then don't just throw it away. You can use the Li-ion cells to make a Do-It-Yourself (DIY) power bank that can charge phones via micro USB cable.

Warning: Please note that breaking open a laptop battery pack is not an easy task. You have to be very careful with the sealed pack. There is no option except cutting open the battery pack's top. Make sure that you do it gently without puncturing the lithium ion cells. A punctured lithium ion cell will catch fire and may explode without any notice. So, before opening the pack train yourself and watch some videos on YouTube to do it safely.

Things You Will Need

  • Digital Multimeter.
  • 18650 Li-ion Cells extracted from laptop's battery.
  • 18650 charging circuit or a power bank case.
  • USB OTG cable (preferably a non-working one): Not needed if you are using a power bank case.
  • Thin wires used for DC batteries (Red and Black): Not needed if you are using a power bank case. 
  • Soldering iron: Not needed if you are using a power bank case.

How To Make a DIY Power Bank With Laptop Batteries

To make a DIY power bank you will need a power bank case. A power bank case comes with a built-in charger, USB ports and battery holder. Though it is a little costlier than the above-mentioned things, but its easy to make a DIY power bank with it. You just have to buy a power bank case and fit the battery in it, its that simple. It comes for 2 and 3 batteries but may be costlier than an actual power bank.

If you don't want to buy this enclosure then please follow our manual tutorial below.

Testing The 18650 Li-ion Cells

In a Multimeter, there are two wires red and black. Connect the red wire to the VΩmA and black wire to COM. Now turn the dial to '20' in DC Volt (DC V as shown in image). Connect the red wire to the positive end of the cell which has a bulge and connect the black wire to the negative end which is totally flat. Read the multimeter reading. If the cell voltage is above 3 volts or above, then it is a good cell otherwise it is a bad cell. Repeat the procedure to identify all the good cells.

Setting Up The Charger Circuit

We are using an 18650 Li-ion battery charging circuit. This circuit charges the 18650 cells and has overcharging protection with LED indicators. Red indicates charging and Blue indicates fully charged. Please see the image below to make the connections.

Warning: The circuit doesn't have a reverse polarity protection. So if you connect the battery in reverse, means positive to negative and negative to positive then the circuit will burn. Use only black and red wire for connections. Red is for positive terminal and black is for negative terminal.

Important Step: You will need an OTG cable to deliver the power to mobile devices for charging. Cut down a USB OTG cable. In it, you will find four wires black, red, green and white. Cut all wires except black and red.

  • B+ : It is an input point. Here connect the positive end of the 18650 cell.
  • B- : It is also an input point. Here connect the negative end of the 18650 cell.
  • OUT+ : It is an output point. Here connect the Red wire of the OTG cable.
  • OUT- : Connect the black wire of the OTG cable.

Note: For making permanent connections you will need a soldering iron. If you don't have any experience of using it then seek the help of an electrician.

Warning: Do not use the soldering iron if you do not know how to use it. There is a risk of electric shock while using it.

Parallel And Series Connections

For our DIY power bank, we will be using parallel battery connection. In a parallel connection, the voltage across the circuit remains the same and its capacity to charge devices increases. While in series connection the voltage increases but the capacity to charge devices remains the same.

Parallel Connection: Parallel connection means connecting positive to positive and negative to negative, and the output is taken across the first positive terminal and the last negative terminal. Suppose you have 3 batteries each of 4 volts and 3000 mAh. So, on connecting them in parallel the resulting voltage will be 4 volts but the capacity will increase to 9000 mAh (3 x 3000mAh). See the image below.

parallel circuit

Series Connection: Series connection means connecting positive to negative, and the output is taken across the first positive terminal and the last negative terminal.Suppose you have 3 batteries each of 4 volts and 3000 mAh. So, on connecting them in series the resulting voltage will be 12 volts (3 x 4 volts) but the capacity will remain the same i.e 3000mAh.

series circuit

DIY Power Bank In Action

You can see the image below showing our DIY power bank charging a Samsung Galaxy phone. Please note that this power bank will charge most phones while they are running. But phones having bigger batteries can only be charged while they are switched off. I have used only one battery but you can connect two more identical batteries in parallel to this circuit.

diy power bank from laptop battery charging galaxy phone

How To Charge The 18650 DIY Power Bank

To charge the 18650 battery connected to the charging circuit you just only have to connect a micro USB charger to the circuit. When you connect the micro USB cable then the Red light will glow on the circuit which means charging has started. When blue light glows then it means that battery has fully charged and you should disconnect the cable. Charging may take 2 hours.

The above DIY power bank can be used to power any USB device that requires a power source less than 4 Volts DC. You can even use it to make a DIY LED torch and charge the battery from your cell phone's charger. 

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  1. sir where do i can possibly get a charging circuit?