I knew I saw a video with 9 volt batteries used for arc welding! During the ongoing discussion about Agent Sonya , using 9 volt batteries as a vacuum tube plate current power supply came up. I found references to doing such a thing on one of Pete's blog post s. I also vaguely remembered a Jeri Ellsworth video where forty 9-volt batteries were connected in series. (The tops of these batteries makes the operation fascinatingly simple.) I finally found the video today. It is amazing! So! We now have visual evidence that nine volt cells can be put to rather spectacular use!