You can also go to endless sphere.com and look up okashira. He sells tesla cells and can make them into what ever pack you want. He will do any S and any P you want. for 40V it would be something like 10S5P for a total of 50 cells and weight about 5.75 lbs. He can also do any connector you want.
I strongly recommend not taking apart dewalt packs unless you are going to be very carefull. You can break the cells if you try to rip off the nickle, so just cut it if you are going to do that. Also soldering to Li-ion cells can damage them, that is why they are all welded. The heat is very quick when you spot weld the cells.
Take a look
Eric