i highly doubt it will work properly with Li-Ion batteries. if the original packs and device were meant to charge and use NiCad's, then there is a high probability it will not work with Li-Ion. i had this same problem in my R/C Cars, i used NiCad sub-c cells forever, and when i got some of the newer NiMH (at the time), my charger would not charge them properly, so i ended up having to buy a newer (and much MUCH better) charger. i'm not entirely sure about Li-Ion, but i would imagine the same rules apply.