Silly wind-up torch but could be anything using Ni-Cad or ni-Mh
multi-cells. LEDs are full bright for a short time after winding up ,
then drops to low light level, regardless of amount of winding beforehand.
One cell is out of kilter with the rest, and in use discharges quickly
compared to the others.
Bench ps charging that one , in isolation, cures the problem.
But presumably it may return , unbalanced charge/discharge across the
cells. How to do the isolated charging of one cell properly, the next
time in the way of monitoring voltages and charge currents ?