Another word of warning.
The old ICOM battery packs consist of 11 NiCad cells producing 13.2 volts nominally, but when charging they are split into one set of six charged in parallel with the other five and uses a ballast resistor to even out the charge currents.
This is why your not allowed to have the radio on while charging as the cells can't be in series and parallel at the same time.
Having said that, if you use a charger of similar output to the standard one, it should be ok.