ORIGINAL: BMT
There is in fact no harm in using Li-Ions as such but based on data at my disposal at the time the state of the art was still in favour of Nicads in terms of current versus voltage. If the KS system is not happy with the battery supply it will respond appropriately.
The high-current draw will presumably be for start & shut-down, just for driving the starter motor ?
Now, you cater for an external 12V supply to be hooked up to the GSU -- so if I understand it correctly then even if there are any issues at all with the high current draw at start & cool-down, then anyone who absolutely wants to use the Duralites to save weight could presumably work any such problem by using the GSU with a small 12V pack for all starts & cool-downs (you could probably even just mount the GSU on a small box containing a suitable external nicad pack).
Gordon