A friend picked up a lot of power-tool batteries at the scrapyard and wants them made into 12V. Remove the BMS from each battery: undo two screws, a little solder on the iron tip, lift with both hands and it comes off; do the same on all of them (cells marked 18650 1500mAh/5C); peel the nickel strip off one by one — careful not to short, this step shorts and sparks extremely easily, one slip and it looks like this (sparks on screen); wipe every cell clean, grind the weld spots off with an angle grinder so they weld well; IR-test each cell’s voltage and IR with the IR meter; pre-cut the strip plus the two main + / − strips. The AWithZ H2 handheld welding pen arrived today, give it a try — long-press the bottom to power on; tack the two ends of the pack first, then weld the whole thing, the welds look very good, 0.12 strip is easy. B+ on the BMS to the positive, held with insulating tape, four wires soldered on; BMS output measures 11.77V, OK; solder the output leads; everyone, do the insulation properly or it will spark; the blue heat-shrink ran out so no shrink wrap. Comments: ‘professional or not, shorted twice’; what use are old batteries; mine is 48V.