Battery packs are very expensive. With this Capacitor discharge welder you can build your own battery packs cheap. This is the only welder that has Pulse width control on the internet. I'm busy with step by step instruction and a schematic to build this welder. I'm done with the control schematic and will post it soon. The above photo's are a rebuild DeWalt 18v battery pack that cost me about $20....a new pack would have cost me $94 + tax.