i have recently bought an 18v panasonic drill and jigsaw,i already owned the panasonic 14.4v impact and sds drills and am wondering if (as the batteries fit in all of the tools) it is safe or advisable(for the tool)to swap them around if the need arose,for example using the 18v battery in the 14.4 impact drill or vice versa,i guess this question would also apply to the festool range as the batteries will fit in all tools.