Building a 16 kWh 314 Ah DIY Home Battery Pack with JK RESS

Steps

1. 1

   Step 1: Unboxing the enclosure

   I open the delivery box to check the contents and show how to build the battery. My first impression is very good because the material is well protected and made of solid metal with neat paintwork. The components are packed in individual boxes and protective plastic.

2. 2

   Step 2: Mounting the side and inner plates

   I start by mounting the first side panel on the bottom. The middle piece sits closer to one side, and this must go at the bottom of the housing. Next, I mount the inner plate inside the housing with the screw holes facing up and the opening to the front, securing it with screws.

   Then I place the next side panel and inner plate on the other side and screw them tight.

3. 3

   Step 3: Placing the fiberglass insulation

   After both plates are in, I place fiberglass sheets against the sides of the housing. I put the long side and the short end pieces in place to prevent short circuits. This creates a solid, well-insulated box for the cells.

4. 4

   Step 4: Placing the battery cells

   I use EVE MB31 cells, which are 314 amp-hours. I place the first cell with its negative terminal in the middle. I put down a plexiglass sheet and place the next cell turned 180 degrees so the positive and negative terminals alternate.

   I continue this pattern for the entire row, ending with a positive terminal.

   What I used

   Item	Amount	Notes
   EVE MB31 cells		314 amp-hours

5. 5

   Step 5: Why EVE cells and DIY

   I use EVE lithium iron phosphate cells because I have always used them in my projects with great experiences. Building a DIY battery gives me control over the brand of cells and BMS used so I can solve faults and replace parts myself. Many commercial solar and battery companies go bankrupt, leaving customers with unrepairable batteries, but with DIY I know exactly how it is built.

6. 6

   Step 6: Mounting the rear wall and top guides

   I insert the rear wall with its raised lip through the housing and turn it upward so the mesh lip sits inside the frame, then screw it from the outside. Next, I place the insulating plates and top guides over the cells and vents. This metal strip plate prevents cells from short-circuiting while keeping the vents open so pressure can escape as off-gassing if anything happens.

7. 7

   Step 7: Connecting cells in series with busbars

   I connect the cells in series by going from the plus of one cell to the minus of the next using the supplied busbars. Since I have the dual-stud version, I secure each busbar with four screws. I use a screwdriver for the video, but I will retighten them with a torque wrench later.

   I carefully repeat this zigzag pattern across all cells while avoiding short circuits.

   Warning

   Always watch out during assembly because a battery stays live at all times with no switch or plug to disconnect, and you can easily cause a short circuit on the cells.

   What I used

   Item	Amount	Notes
   Busbars		Supplied with the set

8. 8

   Step 8: Installing and wiring the BMS

   I install the BMS onto the rear wall mounting place using the provided long thin screws. Next, I plug the four colored connector cables into the BMS. These cables measure the voltage of every cell to prevent over-discharging or over-charging and keep cells balanced.

   They also include thermistors for temperature sensing across four places in the housing.

   What I used

   Item	Amount	Notes
   BMS	1	With connection materials and thermistors

9. 9

   Step 9: Connecting the BMS sensing cables to cells

   I run the ground wire to the first negative of the battery pack. Then I attach the first red wire, B1, to the first positive of the battery using a cable eye under a screw. I repeat this for B2 through B16, connecting each wire to the corresponding positive terminal of each cell in order.

   What I used

   Item	Amount	Notes
   Cable eyes		For connecting wires to terminals

10. 10

    Step 10: Assembling the front panel and terminals

    I remove the protective foil from the front panel and mount the handles using nuts on the back. Next, I mount the battery terminals in the front using sixteen small screws with washers and rubber plates to keep them stable and prevent rattling. I also mount the BMS interface board and display screen from the rear, making sure LEDs line up with the holes.

    I secure the push button through the front hole with a nut on the back.

    What I used

    Item	Amount	Notes
    Small screws with washers	16	For terminals
    Rubber plates		For terminal stability

11. 11

    Step 11: Connecting cables to the front panel

    I plug the wiring harnesses into the interface board, including the flat cable with its alignment notch, the monitor cable, and the on/off switch cable. I rotate my terminals 90 degrees so the supplied busbars fit properly for connecting multiple batteries together.

12. 12

    Step 12: Wiring the circuit breaker and power cables

    I connect a small red wire from the BMS pad plus to the final positive of the battery pack. I connect a short cable to the top on-side of the circuit breaker and a long cable to the off-side, then mount the breaker to the front panel using two countersunk screws from the back. I attach the aluminum busbar and power cable to the positive terminal so energy spreads across both ports for daisy-chaining.

    What I used

    Item	Amount	Notes
    Aluminum busbar	1	For positive terminal distribution
    Power cable	1	55 mm2 original cable

13. 13

    Step 13: Correcting the BMS ground connection issue

    I attach a small busbar plate to the BMS P- minus and connect the negative power cable to use both ports and reduce resistance, then run the BMS negative cable to the housing connector. I point out a fundamental design flaw: the included aluminum ground plate for connecting the BMS B- to the cell studs does not align with the EVE 314 Ah double-stud cells.

    To fix this, I replace the single missing connection with two 25 mm2 cables I had lying around instead of one 35 mm2 cable.

    What I used

    Item	Amount	Notes
    25 mm2 cables	2	Used to replace the misaligned aluminum ground plate

14. 14

    Step 14: Closing the pack and measuring voltage

    I connect the positive cable from the circuit breaker to the positive of the battery pack and place the final busbar. I close the housing and secure the front panel with screws. Finally, I measure the pack voltage with a voltmeter, showing a neat 52.1 volts.

    What I used

    Item	Amount	Notes
    Voltmeter	1	To check initial voltage

15. 15

    Step 15: Starting the BMS and checking cell balance

    I start the BMS by holding down the button. It starts immediately, showing 52.9 volts on the display, which matches the pack measurement of 52.1 volts. The display shows a battery capacity of 40 amp-hours, which is incorrect and needs configuring.

    However, the voltage difference between all cells is a super neat 0.002 volts, proving the EVE cells are 100 percent identically balanced out of the box.

16. 16

    Step 16: Configuring settings via the JK BMS app

    I download the JK BMS app on my phone, search for the battery, and connect. The battery beeps three times to confirm. I verify the password using the default code 123456 to change settings.

    I change the battery capacity from 40 amp-hours to 314 amp-hours and set the cell count to 16 series cells, which updates immediately on the display.

    What I used

    Item	Amount	Notes
    JK BMS app	1	Used for configuration

17. 17

    Step 17: Finalizing the assembly

    With six metal-colored screws and two brackets left over, I note that the brackets can be used if you want to put the battery in a server rack. I carefully place the top lid on the housing while being cautious not to drop the metal lid onto the battery poles, then screw the sides shut. The battery is now fully built, functional, calibrated, and ready to be added to my other batteries for 48 kilowatt-hours of total storage.

    What I used

    Item	Amount	Notes
    Brackets	2	Optional for server rack installation

18. 18

    Step 18: Takeaways

    • Building your own DIY battery gives you full control over components and repairability.

    • EVE MB31 cells arrived out of the box with an incredible 0.002 volt balance.

    • Always exercise extreme caution around live battery terminals during assembly.

    • The JK BMS app requires entering the default password 123456 to modify settings.

    • Correct cell capacity must be manually updated in the app from 40 Ah to 314 Ah.