A stair-climber-specific Li-ion pack; the label reads model 72A, working voltage 39–54.6V, working current <25A, charge 54.6V, no indoor charging; whether 72A is a capacity or a model number is unclear — it doesn’t look that big; the owner says the capacity has faded and it runs out quickly. Cells removed: 18650 at 2000mAh each, 5P for only 10Ah total — not enough, and after several years the fade is severe, completely worthless. Rebuild to the largest size the outer case can take: brand-new EVE 18650 2500mAh, fish paper on every positive for insulation; lay them out to the case’s maximum usable size, 13 series × 8 parallel, 20Ah in total; alternate + / −, with an epoxy board between each series group for insulation; weld with 0.2-thick nickel strip, joining the single cells into one block in parallel and series; once welded, wrap in strapping tape so nothing works loose; fit the BMS (JBD 13S 30A common-port), chosen by cell type, series count and current; after soldering the balance leads, measure the lead order so a mistake doesn’t burn out the BMS; solder the + and − leads; charge/discharge test, and if all is well it’s done. Comments: do you need an electrician’s licence for this? Is this discharge through the BMS but not charge?; requests for a build, phone number, price.