A follower asked whether the UF20B can weld copper stacked directly, I said no, he said support says it can with flux, so here’s the video, see for yourself. The four Jiashikai cells torn down last time (the leaky group out of the 15S is discarded), BMS and charge module not removed, bought a new LiFePO4 board with more ports; two Jiashikai in parallel for a power bank, 30,000 mAh; into the holder in parallel, 3.2V output, spot weld + to + and − to −; many previous copper-and-nickel weld marks on top; switch on the UF20B, charges quickly, try to charge it full before welding; copper 0.1, nickel 0.12 (maybe 0.1, no more than 0.12); added a braided sleeve to the lead himself, No. 6 lead; preheat 10, (interval) 20; straight on first: 0.1 copper + 0.1/0.12 nickel-plated, gear 40 → 70 (dangerous, don’t imitate, same unit as in the showcase): spots are OK but a tug shows they’re not solid, ‘so I don’t recommend copper straight on’; up to gear 90 with four spots, pretty spots but still not solid, don’t recommend stacking copper directly on this model. Next, nickel base: 0.15 nickel-plated steel strip as the base, with experience gear 30 is already very solid (a bit dark, current is high); 0.15 strip at gear 40 tears; up to gear 60 blows two holes; then 0.1 copper on the base: can’t be pulled, can’t be pulled off, clearly far more solid than straight onto the cell; with this model a nickel base works, straight on is not recommended, a thinner strip might stack. After welding, main + / − soldered to B+/B−, an epoxy board sealed on top and glue poured everywhere else; the power bank works, 93% charge; case closed, OK; the two Jiashikai cells sit inside like a single big cell, fast charge, charge board ¥20-odd, wrap with tape; 30,000 mAh, more than enough for food delivery. 68 comments: cells can’t be torn down over and over, three times and they’re basically done; music too loud; will a single layer of 0.3 nickel do; 0.15 copper under, 0.2 nickel-plated on top, weld directly?; can this machine do a 0.2 nickel base; pure nickel costs more than copper strip and doesn’t spark; only this episode showed me copper straight on isn’t stable; 32140 1P16S without a BMS?