A follower from out of town sent in a 48V Li-ion e-bike battery, label says 48V 15Ah Panasonic cells, made 2023-12; it feels feather-light in the hand, clearly not 15Ah, range is very short and nowhere near the kilometres the seller promised. Off with the top cover: the cells only take up a little space in the middle, the rest is foam padding, the block is very small; inside it’s 18650s, 13S3P, the wrappers carry no brand or capacity info — typical knock-off cells, you can imagine the range; this battery is worth nothing. Rebuild as 15Ah: brand-new EVE 18650s at 2.5Ah each, 6P13S; place them in the holder alternating + up / − up, lay one row first as the reference, mind the orientation and don’t get it wrong; snap the top holder on to make one block; the connecting material is 0.2-thick nickel-plated steel strip cut to the needed lengths; the welder is just an ordinary capacitor spot welder — 18650s don’t need much current; 4 welds per cell to guarantee current-carrying strength; weld the parallel and series links in order, then check the whole block for wrong or missed welds; fit the BMS, charge and discharge test, no problems and it’s done. Warning: when buying a battery, any pack whose cells are labelled CATL, Panasonic and the like is fake. Comments (343): how much for a 48V30A build (2); 12C 25P cell config is overkill, 5C is enough (2, doesn’t match this video); selling fakes is a crime, jail (1); which courier did you use (1); how much for 48V25A; how much to rebuild a Sunra; you can tell it’s only a few Ah just by looking.