The 18650 power cell, model, voltage, and internal resistance should be consistent, and the consistency should be better. If there is a voltage detection line, it must be connected to the detection line. Try to use a better battery, don't use a dismantling core. Requires a spot welder.Before replacing the protection board, be sure to measure the voltage of each group of 18650 cells to ensure that the voltages of the cells are consistent. The protection board only plays a protective role and cannot balance the voltage. Because the battery pack cannot be charged or discharged due to the inconsistent voltage of the battery pack, it is useless to only replace the protection board. It is recommended to use new 18650 cellsBL1830 Lithium battery case cover, with LED power indicator, no batterySince the casing is a semi-finished product, it is dangerous to assemble lithium batteries