I have a couple of these (
http://batterytender.com/battery-ten...-at-1-25a.html), and they seem to work fine. I bot some from Summit and the other from a local O'Reilly's...
I enlarged the hole where the negative cable exits from the battery box (located in the trunk of my SPF), and pushed the cable thru. It tucks up nicely when not in use, and I don't have to open the trunk and/or battery box to access it regularly.