The weakest cell sets the pack

by VladM

25 parts

Four cells in series start at 3.3 V. Three hold 6.25 mF and one, cell2, only 5 mF: 80 % of the others' capacity. A 20 mA load drains them all with the same current, so the weak cell falls fastest. Press Run: about 16 seconds later on screen (0.200 s of the circuit's own time), cell2 reaches 2.5 V, U1 throws the load switch and the discharge stops by itself. The run keeps going and the cells hold. A real battery-management system watches every cell; this demo watches only the one known to be weak. The load is an ideal 20 mA source that the switch moves from the pack to ground