#Laptop

An old bank mobile-terminal laptop (card reader, fingerprint) whose battery only showed 4% and would not climb. The creator had turned down re-cell requests before because “brand laptops lock the board when power is cut”, but this battery was already dead, so it was worth a try. Opening the pack: Samsung cells, total voltage looked normal, but per-group readings were 1.790V / 3.395V / 4.11V — left too long, badly unbalanced, scrap. New cells are 2900mAh (original 2600), internal resistance all around 19mΩ; the BMS has current sensing and will limit, so extra capacity would go unused anyway. With the new handheld welder (light) he tried gears 2 through 5 on nickel strip; the whole cell can is negative so no spacer is needed, the positive end gets insulating paper. Along the way: the layout shorts easily, the nickel strip is sharp, and with no jig it is awkward to handle — the three-cell junction was a struggle. Reinstalled, the laptop booted straight up, charge went 6% → 7%, and it did not lock the board after a power-off/on; he cleaned the old glue, checked balance (very consistent), fixed the temperature probe with 704 silicone, and rubber-banded it for a day while the glue cured. Later it showed 0% for an hour (suspected conflict with the BMS); he used the powercfg battery report to read the capacity history. A comment warned that re-celling may still need the battery-management chip (BMS) data reflashed.