Good reading here re battery restoration on my buddy Jim's webpage.

At one point he had a schematic for a desulfator up.

http://www.dallas.net/~jvpoll/Battery/aaDesulfatorSurvey.html

Ah, here we go:

http://www.dallas.net/~jvpoll/Battery/PerformanceDoc23/PerformanceDocumentation_Units23.html