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looking for the cheapest way to weld batteries for rebuilding cordless tool battery packs? Answered


I wouldn't recommend trying, as there is a risk of "frying" (the batteries). Spot welding these things would be tricky without the right tool(s) - i.e. kit like this:


There's plans for a DIY battery spot welder, total cost about $100 if you have to buy everything.


Or the old solution: springs ; )

Interesting, esp. that cluster of MOSFETs.


just solder but prepare both surfaces by scratch it and solder it with the less time possible on the battery or it will be damaged or worse KABOOM! and if it wont stick with it being scratched then use soldering paste or flux.

Er, are you sure you mean "weld"?

Wouldn't soldering be a lot safer, easier and cheaper?

He means spot-weld. Batteries don't solder easily, and they take more heat than a quick spot-weld if you try.


.  Since many battery packs are spot-welded together, he probably did mean weld. But I have to agree with you that, for most DIYers, soldering would be a better option.

I repaired MANY battery packs years ago.  The trick is to find the bad cell.  Thats pretty easy to do. Just measure the voltage on each cell. A good cell will be about 1.2 or 1.3 volts.  There may be several cells that are not taking a charge.  Use a magicmarker to identify each cell that is not measuring up to voltage after charging.  Now you will only remove the bad cells.  When you replace the bad cells with NEW cells, you will need to SOLDER them.  If you can REUSE the old "tabs" thats great.  If the tabe get in your way, just twist them off and solder a wire from cell to cell.  Dont use wire that is too THIN or it will NOT carry the amperage... AND do not use a wire that is too THICK or you will not get the cells back in the case.  I suggest about a 22 gauge wire. You will not be able to solder to the metal unless you use a pointy knife and SCRATCH the surface to be soldered to remove the shiny coating on the metal... Once you scratch through that shiny surface you will be able to solder to it.  Wear SAFETY GLASSES when you solder them because there is SOME danger that the cell could EXPLODE from being soldered/heated too much.  Do this at your OWN RISK if you choose to fix as I suggest.  However, I soldered and repaired maybe 100 of them in my lifetime and NONE of them exploded. ALSO....  DO NOT EVER TRY TO SOLDER TO ANY BUTTON CELL BECAUSE THEY WILL EXPLODE EVERY TIME !!!!!  We are talking about NI-cad nickel cadmium chargable battery packs here, not button cell repairs.