The problem you are having is that the battery is false peaking. The way a charger works for nicad/nimh is it looks at the voltage as the cell charges, and it detects the voltage drop off at the end of the charge. Your battery doesn't have a smooth voltage track so you have to trick the charger by turning up the mV setting so the voltage fluctuations are not enough to turn off the charger.

Conversely, you could join this century and get a lipo powered glow ignitor.