Three or four 9 volt batteries in series is the easiest way to go. In fact it's so easy I've been putting off developing my own design. I do plan on making a rechargeable, portable unit someday soon.
Actually, .999 fine silver is all you really need. By the time we get parts per million of CS, we're talking parts per billion impurities. Parts per tenth billion is not much difference in my book, but won't hurt anything other than your pocket book.
Good distilled water is really important, but boiling is not really necessary (unless you're in a real hurry). Just set it going slow and let it run all day or over night. The slow method makes smaller particles.
For complete details and lots of ins and outs, get my free CS report at Zapperplans.com (link below).