I use a Tecmate Optimate battery maintainer for my XKR. It's a very advanced automatic charger, conditioner, and maintainer. Has never let me down. It restored an old battery for my ride on lawnmower.

I used an Optimate Cable 0-40, Weatherproof SAE socket, panel mount mounted under the rear with the cable fed through the trunk drain hole. I mounted the socket screwed to the corner of a metal plate and used 2 tie wraps to secure it after tightening the screw.

 

I did similar installation with my CTEK...