Decided to go with the Deltran Battery Tender Junior for the XF, about US$27 (shipped) on eBay. Got it, and it is charging. But also just ordered a Deltran 25 foot extension cord ($13 shipped) so that I can permanently attach the battery leads, and run a cord to it with the hood closed (and alarm on) over the winter.

Will use the BatteryMINDer on my other non-sensitive-electronics vehicle, and for desulfurizing my mower's aging battery.