All my cordless tools are Dewalt, five 18V Ni-Cd, five 20V Li-Ion. I started buying 20V brushless when my 18V Ni-cad batteries started petering out, as Desert Rat says. At first I bought adapters for my 18V tools, but that set-up doesn't work well with my 18V circular saw, flashlight, or mini-vac. I the found 18V Li-Ion batteries to fit 18V Ni-Cd tools on Amazon for ~$40 without having to fight those adapters. They have the same shape and dims as the 18V Ni-Cd's, hold a charge for at least a couple months, have 5AHr of power, are extra light weight, have the charge indicator, and charge in my 18V charger. I did find they're not very durable. The first one I bought crashed in my recip saw due to vibration. I sent it back for a replacement and bought a second at the same time. I still have both after two years. I just don't use them in any tools that vibrate. For that I left my adapters in and use my 20V batteries.