DIY 12V 15Ah LiFePO4 Battery Pack With 32140 Cells

In this guide, you’ll learn how to build a 12 V LiFePO4 battery pack using 32140 cylindrical cells.

Materials Used:

1. 32140 LiFePo4 cells - 4 (Link to buy)
2. Insulator ring for 32140 - 4 (Link to buy)
3. 32140 Battery cell holder 2x1 - 4 (Link to buy)
4. Nickel strips 0.2mm 8mm (Link to buy)
5. JBD 4s 20a BMS (Link to buy)
6. Kapton tape (Link to buy)
7. XT60 connector (Link to buy)
8. 12AWG silicon wire (Link to buy)
9. M3 threaded inserts 6mm - 8 (Link to buy)
10. Voltmeter (Link to buy)
11. Tactile switch 6x6x5 (Link to buy)
12. M2 x 4mm screws - 4 (Link to buy)
13. M3 x 10mm screws - 8 (Link to buy)
14. double sided tape

In this project, I’ll show you how to build a 12.8 V, 15 Ah LiFePO₄ battery pack using 32140 cells. Each cell has a nominal voltage of 3.2 V and a capacity of 15 Ah. Since the cells are connected in series, this setup is called a 4S configuration (“4 in Series”).

If you want more capacity, you can easily expand the pack. For example, adding another identical string of four cells in parallel creates a 4S2P pack (4 in series, 2 parallel strings), doubling the capacity to 30 Ah. Also make sure to choose an appropriate BMS.

Cell datasheet

There are many low-grade or used cells in the market, so it’s very important to buy from a reliable source. Always try to get cells from the same batch and with similar internal resistance. I asked my vendor to confirm both the manufacturing date and the internal resistance before buying. After receiving the cells, I checked the voltage of each one and confirmed that they were all at a similar voltage level.

Even though the cells were at a similar voltage, I connected them in parallel and top-balanced them to 3.5 V.

Next, I added insulator rings on the positive terminals, placed the cells in the holder, and spot welded them in series with nickel strips.

After that, I wrapped the cells with Kapton tape for an extra layer of protection. I also 3D printed a base for the BMS, but you can use a plastic sheet or any other insulating material instead.

I fixed the JDB 4S 20A BMS onto the 3D-printed base with double-sided tape. Then I soldered all the wires to the battery pack according to the circuit diagram given above. Then I wrapped one more layer of Kapton tape. For the main output wires, I used 12 AWG wires and an XT60 connector.

I 3D-printed a simple case for the battery pack. To monitor the voltage, I used a voltmeter with a push-button switch. The voltmeter can be directly screwed to the case using M2 screws. For the switch, I soldered it to a small PCB and mounted that PCB onto the case.

The wiring is straightforward: the negative wire from the voltmeter connects directly to the battery pack’s negative terminal, while the positive wire goes through the switch before connecting to the battery pack’s positive terminal.

Finally, I fitted the battery pack into the case and used double-sided tape to keep it snug. Then I closed the case cover and secured it with M3 screws. I also applied some hot glue on the wires to prevent them from being pulled.

To charge the pack, I set my power supply to 14.4 V with a constant current of 5 A. After charging, the battery pack is ready to use.