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It's not recommended, but I have soldered in replacement cells with a regular 30W iron. It can be as easy as open the pack, identify and replace bad cells, man

It's not recommended, but I have soldered in replacement cells with a regular 30W iron. It can be as easy as open the pack, identify and replace bad cells, manually balance charge the cells (one at a time), tape the pack back together. It's a bit janky, because the plastic cases are sonic welded and you have to butcher them a bit to get them open and then glue or tape them back together, but it can be difficult to locate batteries for old laptops and I don't want to spend money.

StavrosK 6y ago
The problem with soldering them with an iron is that you get the cells way too hot by the time solder has managed to melt, even if you're quick about it.
- jacob019 6y ago
  Not if you work quickly and use 63/37 0.6mm rosin core tin-lead solder with a 30W iron. I never need to apply the iron for more than half a second. I've done this more than a few times, and I realize that it goes against standard safety recommendations, but I'm going to keep doing it. And if you're recycling cells from other packs, they are likely to have remnants of old tabs still connected, so you can solder to the tabs instead of directly on to the cells, which gives a little more thermal wiggle room.
- samatman 6y ago
  You can also stick the cells in the freezer before soldering. It adds a fraction of a second to coming up to temperature, and gives the cell proper a lot more thermal wiggle-room. Nothing bad will happen if you keep them above about -20° C. Definitely file this under "bad advice you probably shouldn't follow, and don't tell them I sent you", but 'allegedly' this works...
  - mschuster91 6y ago
    That's extremely, extremely risky to do if you don't know the cell's composition, especially the liquid electrolyte, and its performance in cold temperatures. Last thing you want to do is manage to get it frozen and physically damage the layers.
    - samatman 6y ago
      Yes, you should look it up, and pretty much any 18650 will have -20° C or lower as the lower end of its range. It would be extremely, extremely risky to sell a product which could be destroyed by leaving it in the car in the winter. I think this advice only earns one "extremely" or maybe a mere "very"...
- jve 6y ago
  What are the consequences of getting cells too hot by soldering? Immidiate danger or danger while discharging/charging?
  - jacob019 6y ago
    immediate danger

StavrosK 6y ago

The problem with soldering them with an iron is that you get the cells way too hot by the time solder has managed to melt, even if you're quick about it.

jacob019 6y ago
Not if you work quickly and use 63/37 0.6mm rosin core tin-lead solder with a 30W iron. I never need to apply the iron for more than half a second. I've done this more than a few times, and I realize that it goes against standard safety recommendations, but I'm going to keep doing it. And if you're recycling cells from other packs, they are likely to have remnants of old tabs still connected, so you can solder to the tabs instead of directly on to the cells, which gives a little more thermal wiggle room.
samatman 6y ago
You can also stick the cells in the freezer before soldering. It adds a fraction of a second to coming up to temperature, and gives the cell proper a lot more thermal wiggle-room. Nothing bad will happen if you keep them above about -20° C. Definitely file this under "bad advice you probably shouldn't follow, and don't tell them I sent you", but 'allegedly' this works...
- mschuster91 6y ago
  That's extremely, extremely risky to do if you don't know the cell's composition, especially the liquid electrolyte, and its performance in cold temperatures. Last thing you want to do is manage to get it frozen and physically damage the layers.
  - samatman 6y ago
    Yes, you should look it up, and pretty much any 18650 will have -20° C or lower as the lower end of its range. It would be extremely, extremely risky to sell a product which could be destroyed by leaving it in the car in the winter. I think this advice only earns one "extremely" or maybe a mere "very"...
jve 6y ago
What are the consequences of getting cells too hot by soldering? Immidiate danger or danger while discharging/charging?
- jacob019 6y ago
  immediate danger