A customer sent in a 48V e-bike battery case whose cells were dead. The creator measured the inside (130 × 370), worked out that 13S6P would fit, and chose EVE 2.5Ah 18650s — 78 cells for 48V 15Ah. Cells go into the holder alternating positive-up / negative-up (parallel across, series down), get spot-welded into one block with 0.2mm nickel-plated steel strip on both faces, with the main positive and negative brought out separately. The pack is wrapped in strapping tape, the BMS is fitted with its balance leads soldered to each series group in order, the input/output leads are connected, and a charge/discharge test (49.14V / 6.50A on screen) is run before delivery.