Thanks for the comments. After I posted the message on this forum I searched on Usenet and found many discussions on desulfation battery chargers. Although it's definitely not scientific proof, it seems that most people think these kind of desulfation chargers are snake oil. There doesn't seem to be any independent proof that these kinds of chargers are really beneficial. And the desulfation process seems to have many fine print caveats. Again, this is based on user comments on Usenet.

I'm going to stick with Battery Tender. Now I'm unsure if I want the Battery Tender Plus or the Jr.

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Dave

1998 E320
2001 SLK320
2000 Lexus RX300