The flashlight dies in under two hours; opened up (pull forward, no screws) it turns out to be built cheap: a single 14500 400mAh NMC cell. He swaps in a 2000mAh 18650 that just fits. These cells are hard to solder (flux would help), so the creator first spot-welds a nickel tab on each end to try out the new mini welder (easy to carry, compact), in manual mode. 11 gears: top gear first to see its power — it holds firmly but punches two holes through the 0.12 nickel strip; then welded onto the cell it holds well. Thick strip takes the top gear, thin strip the middle; the higher the gear, the more power it uses. Gear 1 test: 0.12 strip peels off (not good), but very thin strip holds even on the lowest gear. Note: don’t force it down, keep the surface flat and just make good contact, or you’ll punch through. Cell swapped, OK.