I use to buy them by the case at Harbor Freight Tools to give away to my customers when I owned a battery co. Buy a battery and get a free "maintainer"!!!. The ones with the direct hook up to the terminal with a disconnect are a little more "sure" that the cig lighter style. I use to pay about $2 - 3 dollars each. They are also called "float chargers" Sold that company in 03 and I am sure the price is up a bit now.
I heard that it won't work with the new spider though .
I got an eyeball on one, working out numbers. I should just replace the schumaker, you're right. I shouldn't let it touch a new car after being used on the 986, might catch m96 motoritis.
I use a Deltran Tender Plus. They have three or more models and they work great. When I'm going to be out of town for a month or more, I hook mine up and never worry.
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Denver Steve
Carrera, Cabriolet, 6-Speed, Black/Tan