Weeks ago a YouTube link was posted which left another link, as they do, and this was about converting an electric drill to lithium. It stuck in the back of my mind. Last week I needed my old 24V NiCd drill, one battery totally knackered, other not too bad. Then DING that memory. I had some 11V Lion batteries for model helicopters, one pair relatively small capacity but bigger than the NiCds. Worth a try I thought. 2 batteries fitted perfectly in the space of the NiCds, wire it up - perfection. The NiCd lasted an hour or so, the Lithium all day. Down side is I have to use the model battery charger, which is switchable to 22V but it charges many times quicker than the NiCd one. Also there is no protection for over discharge so it's up to me to spot this. So not viable economically if you don't have the kit in stock ( it would cost £75 ) but works if you do. One amazing fact is the weight difference, the NiCd must be 3 times heavier.