+T for the good name!
In short, I made my own 18v box by simply hooking two 9v in series. In more detail, I made my own battery box which runs on a regular 9v battery (I think it's very similar to the SPSB-1). Then, by using those 9v battery terminals that you can find at rat shack, I connected the two 9v's together and connected them to the batt box. I then used packing tape to physically (not electrically) hold the two 9v's together. Now, two 9v's won't fit inside my batt box, so I just used more packing tape to hold the batt's against the box. I tested both the 9v and the 18v batt box with my car stereo, which puts out decent bass SPL. It was clear that the 18v worked better.
Now, I don't know if I would recommend 18v for just any mic, but I know it works well for the AT853. But I would recommend experimentation! Maybe your friend had a mic that's incompatible with anything above 9v. I do have some old generic mic that came with my Sony WM-D3, and it didn't like 18v (the noise floor shot up through the roof).