The creator builds a 48V LiFePO4 battery for an e-bike that has run on lead-acid for three or four years: 16 × 3.2V/15Ah cells all in series come to exactly 48V. To carry more current he stacks copper strip on nickel strip, and first tries two machines: the self-built welder welds 0.12 nickel-plated steel strip + 0.1 copper, the handheld welder welds 0.12 + 0.05 copper, both solid, and he mainly uses the self-built one (it can weld thicker copper). All 16 cells read 3.297V with 1.7–2mΩ internal resistance, so he builds without balancing. Triple holders are assembled (one holder with four extra corners wouldn’t fit and got trimmed), insulating paper applied, nickel and copper strip 15mm wide, the nickel strip’s sharp corners trimmed on the positive side; the jump starter that powers the welder is put on charge. During welding the self-built machine (with added capacitors, shortened leads and swapped MOSFETs), its thermal pad, the jump starter and the cells all get too hot to touch, so he keeps stopping to cool them with a fan; the jump starter won’t charge at 5V2A, so he pulls the 60V/20A Bluetooth BMS (switchable NMC / LiFePO4) from a previous 21700 pack. After several ‘won’t weld’ episodes he finds he had stacked two layers of copper by mistake; later he adds nickel strip to compensate. Main + to main − reads 52.7V, total internal resistance 32mΩ. 704 silicone to fix, mesh double-sided tape for the ribbon, sense leads soldered group by group and tinned (‘nearly had an accident’), lead order checked, 3 hours 40 minutes in total; the Bluetooth app gets LiFePO4 settings: over-voltage 3.65, under-voltage 2.3, balancing from 3.5; insulating board, main positive and temperature probe go in, insulating paper on, and heat-shrink film can be done with a hair dryer (keep it out of the sun). Lead-acid measures 89mΩ for comparison; the battery bay is bigger than expected (would take 48V30Ah); adhesive-lined heat-shrink for waterproofing; on the bike the app shows 53.0V, -16.5A, 14.8Ah, 0.038V delta, 0.9kW. LiFePO4 isn’t ideal for northern winters, but it’s cheap, safe and fades less than lead-acid. The top comment says the video is too long.