Introduction: Snap-on Battery Repair/Repacking

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My Snapon CTB7185 battery was getting a red light on the charger that prevented charging. Instead of paying $190 for a new one I decided to try repacking the battery. This project requires a good spot welder which is only worth it if you have many batteries to repair.

Supplies

  • High powered soldering Iron
  • Spot welder
  • Side cutters
  • 0.2mm pure nickel 2P belt
  • Silicone
  • Kapton tape

Step 1: Warnings

Working with lithium batteries can be extremely dangerous. There is a lot of energy stored in a small area and improper handling can result in fire and personal injury. Before starting:

  1. Clean your workbench so there is nothing that can tip over / fall / or get bumped and short connections
  2. Remove all jewelry! Rings and chains will short out connections and get welded to the battery
  3. Discharge the failed battery as much as possible before starting

All of the tools we will be using are metal, do not bridge any of the cells. Cover nearby cells with Kapton tape or electrical tape to prevent accidental shorts.

Step 2: Shell Disassembly

Start by removing the 4 torx screws holding the shell together.

Once the screws are removed there is nothing else holding the pack together. Turn the shell upside down and the batteries, battery holder and circuit board will come out as one piece.

Step 3: Removing the Old Cells

This is the most dangerous part so please pay extra attention to every move you make

We need to break the spot welds off the old cells to remove them from the cell holder. I will be replacing the nickel strips so I don't worry about saving them. Cover adjacent cells with Kapton or electrical tape to prevent accidental shorts before the next part.

Take side cutters and lift up the edge of the nickel strip. Rotate the side cutters and peel the strip away from the battery. This may take some force but remember to roll the side cutters and the welds will break.

On the positive side of the cell only the center is positive. The outside perimeter is still negative. Do not pry against the perimeter when working on the positive side of the cell. After the welds are broken use a soldering iron to remove the nickel strips from the circuit board. The cells are held in with silicone, use a non conductive rod to push them out from the negative side.

The cells are Moli IBR-18650B and they are rated at 1.5Ah, 25A

Step 4: New Cells

I decided to salvage cells from a new Harbor Freight Bauer 20V 3Ah battery. They go for about $45. Harbor Freight uses Samsung INR18650-15M which are rated for 23A and 1.5Ah

There are other options for cells, MOLICEL P26A would be a good choices that would increase the capacity. Your batteries need to be able to handle high current, especially for something like an impact.

Be very cautious of batteries from Amazon or eBay. I tested some cheap batteries and they only had 0.1Ah capacity and 1A discharge. Buy real batteries from a reputable source, I have experience with liionwholesale and have not had a problem with them yet.

Step 5: Assembly

Insert the new cells into the cell holder with a bit of silicone to keep them from moving around.

This next part requires a spot welder. I tried a cheap eBay battery powered welder and it was not powerful enough for 0.2mm strips so I ended up purchasing a quite expensive unit called the kWeld from Keenlabs for $200usd shipped. The Welder requires a high current source so I am using a 340CCA 12V lead acid battery, I am only able to reach 1000A weld current but it was giving good results. You could use an RC battery like the Turnigy nano-tech 3S/5000mAh/130C to reach the higher current of 1500A that is recommended.

Using the 0.2mm 2P nickel belt cut off enough for 3 pairs of batteries. Trim one side around the slots and fold it over like in the picture. The folded side will be soldered to the circuit board.

You must solder the connections from lowest to highest voltage.The circuit will prevent the tool from operating if you do no connect them in order. The order is shown in the picture, voltages are for fully charged cells.

Do not forget to attach the temperature sensor to the battery with silicone or Kapton tape

Reassemble the shell and place it on the charger until charged.