Introduction: How to Make a 12V Lithium-Ion Battery Pack at Home Using Old Laptop Cells

By ER GREAT YouTube Channel
About: 👋 Hi there! I’m Kishor Kumar I’m an electronics enthusiast, maker, and YouTuber who loves bringing creative ideas to life through DIY electronic projects. My projects blend innovation, sound, and visual effect…

Lithium-ion batteries are everywhere—from laptops to power banks—and the best part is, even old or dead laptop battery packs often contain perfectly working cells inside. Instead of throwing them away, we can recycle these cells and build a powerful, compact, and long-lasting 12V Li-ion battery pack at home.

In this project, I’ll show you how to create a 12V rechargeable lithium battery using recovered 18650 cells from an old laptop battery. This method not only saves money but also improves efficiency, just like the 20,000 mAh DIY Power Bank we built earlier.

By following simple steps—testing cells, balancing them, arranging series connections, and adding a BMS—you can build a safe and reliable 12V battery pack perfect for:

  1. DIY electronics
  2. Solar projects
  3. LED lighting
  4. RC/Robotics
  5. Emergency backup power

This tutorial is beginner-friendly, budget-friendly, and a great way to give new life to old batteries. Let’s start building your own high-performance 12V Lithium-Ion Battery Pack!

Supplies

  1. Old Laptop Batteries (18650 Cells) – We will recover and test good cells from old laptop battery packs.
  2. 3D-Printed Cell Gaper / Base – To hold all cells tightly in place and maintain proper spacing for heat dissipation.
  3. Copper Wire or Nickel Strip – For making strong and low-resistance connections between cells.
  4. Multimeter – Essential for checking cell voltage, testing capacity, and eliminating bad or unsafe cells.
  5. 3S 10A BMS (Battery Management System) – To protect the battery pack from overcharge, over-discharge, and short-circuit.
  6. Soldering Iron / Spot Welder – For securely connecting cells (spot welder preferred for safety).
  7. Insulation Tape / Kapton Tape – For electrical insulation and extra safety.
  8. Hot Glue or Adhesive – To fix the cell holder and wiring firmly.
  9. XT60 Connector / DC Output Wires – For connecting your 12V battery output to other devices.

Step 1: Collect and Extract Cells From Old Laptop Batteries

To begin this project, take any old laptop battery packs—typically 6-cell or 4-cell configurations. You can easily gather or purchase these from a local laptop repairing shop, where they are usually available at a very low cost. These cells are original and generally far more reliable than many cheap, counterfeit cells found in the local market.

Start by carefully opening the outer plastic casing of the laptop battery. Use a flat screwdriver or a pry tool to split the seam and slowly work your way around the edges. Once the cover is opened, gently remove each 18650 lithium-ion cell one by one.

Most laptop batteries have cells stuck together with glue. Clean this glue using thinner or petrol to make the cells neat and ready for testing. Make sure to handle the cells with care during extraction—sharp edges and metal tabs can cause cuts, so work slowly and safely.

After removing and cleaning the cells, keep them aside for testing in the next step.

Step 2: Test and Charge All Cells Properly

Once the cells are cleaned, the next step is to test every single cell using a multimeter. This helps you identify which cells are good, weak, or completely dead.

  1. Check Initial Voltage:
  2. Place the multimeter probes on the positive and negative terminals of each cell.
  3. If a cell shows some voltage (above 2.0V), it is likely usable.
  4. If a cell shows 0V or no reading, it might be deeply discharged.
  5. Revive Low-Voltage Cells:
  6. Cells showing 0V can be tried once more by giving them a small boost charge.
  7. Charge these cells for a while and then check the voltage again.
  8. If the voltage appears after charging, you can keep the cell for further testing.
  9. If the voltage still remains 0V, then the cell is unsafe and must not be used.
  10. Fully Charge Each Cell:
  11. Use a TP4056 Lithium Charging Module to charge every cell one by one to full capacity (around 4.2V).
  12. This is a very important step because:
  13. Cells must be at the same voltage level
  14. It improves performance
  15. It ensures safety and long battery life

Step 3: Prepare the 3D-Printed Cell Gaper / Holder

To arrange all the lithium-ion cells neatly and safely, you will need a cell gaper or cell holder. This helps maintain proper spacing between the cells, improves airflow, and prevents heating issues.

You can 3D print the lithium cell gaper if you have access to a 3D printer. Many ready-to-print designs are available online, and they ensure the cells fit securely in the correct alignment.

If you don’t have a 3D printer, no problem—you can simply buy a cell holder from the local electronics market. These holders are inexpensive and come in different sizes to match your 3-cell, 4-cell, or 6-cell arrangements.

Once you have the cell gaper ready, place hook all 3D printed gaper together in 6x3 Pattern in two pieces.

Step 4: Arrange Cells & Build the 12V Battery Pack Using a 3S 10A BMS

Now it’s time to assemble the actual 12V Lithium-Ion Battery Pack. For this, we will use a 3S 10A BMS (Battery Management System) which will protect the battery from overcharging, over-discharging, and short-circuit conditions.

  1. Place All Cells in the Gapper Tray
  2. Arrange all 18 cells properly inside the 3D-printed or purchased gapper tray. Ensure the positive and negative terminals are aligned according to the 3S (Series) configuration shown in the circuit diagram.
  3. A 3S pack means:
  4. 3 groups in series, each group containing several cells in parallel.
  5. Make Cell Connections
  6. Ideally, nickel strips and a spot welder offer the safest and most reliable method for connecting 18650 cells. If you are using nickel strips, spot weld them exactly as shown in the circuit diagram.
  7. This ensures:
  8. Lower resistance
  9. Strong bonds
  10. Better lifespan of the battery pack
  11. Using Copper Wire Instead of Nickel (My Method)
  12. In my build, I am using 2mm thick copper wire instead of nickel strips.
  13. Bend the copper wire according to the series and parallel circuit layout
  14. Heat the wire properly and solder it firmly to the cell terminals
  15. Make sure each joint is strong and does not heat excessively during soldering
  16. Note: Be careful while soldering directly on cells; work quickly to avoid overheating the battery.
  17. Connect the 3S BMS
  18. After all cell connections are completed, take your 3S 10A BMS and connect it using the same thick copper wire for better current flow and higher efficiency.
  19. Follow the BMS wiring diagram correctly:
  20. B- goes to the main negative of the battery pack
  21. B1, B2, B3 go to the series connection points
  22. P+ and P- will be your final output terminals

Once everything is wired correctly, re-check all connections to make sure there are no loose joints or short circuits.

Step 5: Final Testing & Output Verification

Now your 12V lithium-ion battery pack is fully assembled and ready for testing.

Take your multimeter and check the output voltage of the pack.

  1. If the reading is above 12V, your battery pack is perfectly built and ready to use.

You can place this battery pack inside a battery enclosure for protection and a cleaner look.

Otherwise, you may keep it as it is, but make sure all terminals are insulated properly.

For load testing, as shown in the example, I connected a 12V–22V (200W) DC Boost Converter, and used a 100W bulb as the load. The bulb glowed perfectly, proving the battery pack is supplying stable power.

Your battery is now ready to be used in any project that requires a 12V DC power source.


Benefits of This DIY 12V Lithium-Ion Battery Pack

  1. Cost-Effective: Reuses old laptop cells, making this battery much cheaper than buying a new lithium pack.
  2. High Efficiency: Lithium-ion cells offer better performance and longer life compared to lead-acid batteries.
  3. Lightweight and Compact: Very easy to carry, mount, or store compared to heavy 12V SLA batteries.
  4. Rechargeable & Eco-Friendly: Extends the life of discarded laptop batteries, reducing e-waste.
  5. High Output Current: With thick copper connections and a 10A BMS, the pack can power heavy loads.
  6. Customizable: You can increase or reduce cells based on your required capacity.
  7. Long Life Cycle: With proper charging and protection, these cells can run for hundreds of charge cycles.


Step 6: Applications of the 12V Battery Pack

This battery pack can be used in a wide range of DIY and professional projects, such as:

  1. Solar Power Systems
  2. LED Strip Lighting / Emergency Lights
  3. DC Fans & Small Appliances
  4. DIY Power Banks & UPS Systems
  5. Robotics and RC Projects
  6. Electric Bicycle / Scooter Testing (low-power applications)
  7. CCTV Camera Backup Power
  8. Portable Tool Power Supplies
  9. Car/Bike Accessory Power Source
  10. 12V to 24V Booster Applications


Step 7: Conclusion

In this project, we successfully created a 12V Lithium-Ion Battery Pack using recycled 18650 cells from old laptop batteries. By testing, balancing, arranging in a 3S configuration, and adding a 10A BMS, we built a powerful, safe, and long-lasting battery pack at a very low cost. This DIY method not only saves money but also gives new life to unused cells, reducing e-waste and improving efficiency.

The final battery pack delivers stable power, handles high load, and can be used in multiple applications like solar setups, lighting systems, DIY electronics, and more. With proper charging and handling, this pack will serve as a reliable 12V power source for many future projects.