Snap-on Battery Repair/Repacking




Introduction: Snap-on Battery Repair/Repacking

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.


  • 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.

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    Question 21 days ago on Step 4

    Hi! The INR-18650-P26A have been Discontinued. Will the new Molicel P28A 18650 2800mAh 35A Batteries Will work as well?


    Answer 21 days ago

    Yep, the specific battery isn't too critical as long as it can do around 25A continuously.


    Reply 21 days ago

    Thanks for your fast reply. One more question. The 0.2mm 2P nickel belt have what dimensions? I found this one on Amazon: Hilary 5M 2P 21700 0.2mm Pure Nickel Belt Spot Welding Machine Spot Welding Nickel Belt


    Question 10 months ago

    Hey thank you for posting about this. I just rebuilt my 8185 battery pack and now I'm getting the right voltage output on the 2 outer connectors where the battery connects to the impact but now I'm not getting any voltage out of the middle connectors. It's showing full voltage on the battery gauge but when I plug it into my impact and pull the trigger, the led light on the impact comes on but the impact will not operate. Any idea what I've done wrong? Thanks in advance


    Answer 10 months ago

    Easiest thing to try is to put it on the charger for a couple minutes or maybe even to full. If that doesn't work unsolder all the voltage sense terminal tabs from the PCB and re-solder them in order from minimum voltage to maximum voltage. My control pin does not show any voltage. Measuring between (N1 to +) and (N2 to +) are both just under the pack voltage ~19V


    1 year ago

    It would be nice too if you could use LFP (LiFePo4) cells .They have a lower voltage but much longer recharge cycles so they last 3 times as long at least .
    If you want to know more go here and join.


    Tip 2 years ago

    When the chargers refuse to charge the packs it is usually because the pack voltage has dropped too low . Use a power source ,car battery ,lab,computer etc to add a charge across positive and negative terminals of the pack to get the voltage back up a bit . Usually only needs a 30 second charge ,then put it on the charger again . That usually does the trick and gives the packs extra life.

    Work out a way to only charge the packs to 90% and you will double the life of them . Its charging to 100% all the time that kills them,phone and laptop batteries also.