DIY Dewalt Battery

You cannot combine parts from this model with an original battery for repair or modification. It will not fit.

This design is intended for 21700 cells, but 18650 cells will work. This comes with 5 and 10 cell options as well, so there are 4 types of battery you can build using this model

• 5 cell 21700
• 5 cell 18650
• 10 cell 21700
• 10 cell 18650

The size will be the same regardless of using 18650 or 21700.

I recommend building a 5-cell 21700 battery. I made 2 of these and have been very happy with their performance. I have dropped, hit, and generally abused them over that time. By sourcing your own high quality 21700s you can get double the energy storage and power output compared to the Chinese 18650 batteries that typically come with new dewalt tools, for almost the same size and weight.

Please be aware of the drawbacks of building a 10 cell 21700 battery. The print will be more likely to break when dropped, and you might not be able to take advantage of dewalt's fast chargers. Dewalt uses a different BMS board for their large batteries. If you decide to make one anyways, please let me know how it goes and if you can fast charge it, and I will update this description.

Materials:
- Four M4 screws (20mm length for 5 cell, 40mm length for 10 cell)
- One small spring
- tube of silicone (caulking or RTV)
- either five or ten 21700 or 18650 cells
- a Dewalt BMS board

The total cost can be less than $30 if you get a good deal on cells or already have some. Some good 21700 cell options are Molicel 21700 P45B, Samsung 30T, Samsung 40T, or Samsung 50S. Any cell with a rating over 20 amps works. Do not use old laptop cells.

Rough Instructions:

1. Check cell voltages are within the same range. If their voltages are too different the battery will not charge.

2. Insert the cells into the holders alternating positive and negative

3. Spot weld or solder very thick nickel strips or copper wire to the cells to form 1p5s or 2p5s config. This needs to carry a lot of amps so make sure the connection is good.

4. Roughly follow my wiring instructions diagram and attach the BMS/terminals to the top rack with glue, or use a soldering iron to melt the plastic together. Solder the BMS wires and power leads. You can see if the BMS is working by pushing the button on the LED board.

5. Just for testing, put the case together starting by placing the soldered assembly into the bottom part. Place the LED board and the battery level button print into their slots. Get the release button in place with a spring on the circle area of the top rack. Screw the top case shell into place. Check the fit and make sure no wires are pinched.

6. Test the battery to make sure it charges full and works with your tools. This is the last chance to fix any mistakes.

7. Disassemble and use silicone glue to fill in all the empty space in the battery. The more glue you use the stronger the battery will be. The important areas to glue are the corners and the area around the battery terminals where the tool holds onto the battery. If you drop a tool and the battery hits the ground first, this is where all the force is concentrated. Do not glue the release button or spring.

8. Reassemble and double-check check no wires are pinched in the process. Let the glue harden.

Example links to items you need. I have no affiliation with these and you should be able to find cheaper or more local listings.
BMS board:
https://www.aliexpress.us/item/3256805535552741.html
https://www.aliexpress.us/item/3256803602190043.html

21700 cells:
https://www.18650batterystore.com/products/samsung-40t
https://www.18650batterystore.com/products/molicel-p45b

Silicone (kitchen and bath caulking or RTV is fine):
https://www.homedepot.com/p/GE-Silicone-1-10-1-oz-Clear-All-Purpose-Caulk-2708911/100091111
https://www.amazon.com/Permatex-80050-Silicone-Adhesive-Sealant/dp/B0002UEPVI/

Springs (10mm diameter or smaller, around 14mm height):
https://www.aliexpress.us/item/3256801222091501.html?

TOP, BOTTOM, and BUTTON parts need supports to print.

I recommend printing in ABS, nylon, or polycarbonate because they have much better impact and heat resistance.