Been a while, but as far as I remember its to do with the difference's between chemistries, NiCad, Ninh and LiIon, Nicad can normally only be charged at approximately 10% of its total capacity if you want it to last, Ninh can charge at a higher rate if it's chemistry can take the higher charge, its to do with the Cathode construction, LiIon have to be balanced charged on each individual cell, if it indeed has more than one cell, unfortunately LiPolymer cells which where the first high capacity cells had a tendency to catch fire if the wrong charger was used additionly whilst burning could supply its own Oxygen by chemical reaction to keep it burning, I have been using all of these Chemistries for a number of years in RC equipment so I got used to the requirement of the different chemistries and their differing requirements for charging, the most modern of these, the LiIon is by far the safest but do need balance charging, to prevent premature failure, this is normally built into the device being charged, bare multiple cells need a special ballance charger.
Mike
