If you over-discharge Lipo batteries, you can end up with dead cells that read zero volt and cannot be re-charged again. In this post I documented how I repaired/fixed a LiPo battery by removing the dead cell.
Disclaimer: I DO NOT recommend doing this, it’s very dangerous working on defective LiPo. The author and OscarLiang.com are not responsible for any fires or damage caused.
If you have a battery with dead cell, it’s best to just dispose of it, guide: how to dispose LiPo batteries.
Note that by removing a cell from LiPo battery, the nominal voltage also decreases – e.g. a 4S becomes 3S. It’s possible to make a good working LiPo using good cells from LiPo batteries of the same brand/specs in order to maintain the save cell count.
I don’t think it’s a good idea to mess with LiPo, but if you must, do this outdoor to avoid burning the house down, or filling your house with toxic gasses from LiPo fire.
- A multimeter to check battery cell voltages
- Wire cutter
- Stanley / Craft Knife
- Soldering iron (recommendations)
- Hot Glue or Liquid Tape
- Electrical tape
- 80mm PVC heatshrink tube/sleeve
- A big bucket of sand to put out fires (just in case!)
Step 1 – Removing heatshrink and tapes
Remove the exterior plastic packaging from the LiPo battery. Make sure you are cutting on the side with the internal protective layer. This thicker flexible layer will help ensure that you do not puncture any of the cells with your knife.
Remove the tape wrapping around the cell terminals, then unsolder the balance wire and XT60.
Step 2 – Separating the bad cells from the good
Separate the good cells from the bad with a plastic tool, do not use metal to avoid puncturing the cells. When taking the cells apart, working in a warmer room help separating them more easily because the adhesive is less sticky when warmed up.
Use a multimeter to determine if the cell is bad or not.
If the cells next to each other are good, then you don’t need to separate them, just leave them bundled together.
I also mark the good cells with “OK” in case I forget which is which :)
Step 3 – Putting good cells together
Check with a multimeter which terminals are positive and negative, remember the cells must be wired back together like this: + to – to + to – to + to – to + to –
Then I solder the cells side to side in series: + to – to + to –
Step 4 – Soldering wires
When soldering on batteries terminals, you need to be extremely quick, and use lower temperature for soldering. Don’t overheat the battery, otherwise it might cause a fire if you are not careful.
- Solder the main connector lead (XT60) to the Lipo cells, red to cell 1 positive, and black to cell 4 negative (as shown in Pic 1)
- Then the balancing lead following the wiring schematics diagram above. Starting with negative wire: first black balance lead connects to the negative of the 4th cell. (Pic 2)
- 2nd black lead goes to – of the 3rd cell, or the + of the 4th cell (Pic 3)
- 3rd black lead to – of the 2nd cell, or the + of the 3rd cell (Pic 4)
- 4th black lead to – of the 1st cell, or the + of the 2nd cell
Lastly, the red balance lead goes to the + of the 4th cell. Then secure the solder joints with some hot glue.
Step 5 – Final check and re-packaging
Check the voltage of the discharge connector, as well as the voltage of the balance plug, make sure each cell is reading the correct voltage.
If you are just removing a dead cell from a 4S LiPo like I did here, you can re-seat all the balance wires in a new 3S balance connector, or just remove the unused balance wire like so.
Now it’s a working 3S LiPo.
PVC heat shrink tube is great for re-packaging LiPo (80mm heat shrink is great).
You can remove and save connectors / balance lead from old or dead 2S or 3S LiPo’s. If you have a 4S with a dead cell or two, you can convert them to a 2S or 3S pack. They are great to be used with your FPV goggles and TX.
- May 2016 – Article created
- July 2018 – Updated
- May 2021 – Added more pictures, updated post
Co-author: Hans Turpyn