Hi Paul, welcome to the wonderful world of XKR motoring, I hope you have many happy, top down miles.
The answers above are good, but my recommendation is to use the charger connected as follows:
Lift the boot floor and you will see an earth connection - looks like a threaded screw coming up from the boot floor - down on the left hand side as you look forward. Ensure you remove the paint to get a proper connection to earth / ground, fit the black clip.
Remove the vent louvre on the left hand side panel of the boot as you look forward and, with a torch, check inside and down for the battery remote positive cable, which should have its termination covered with a rubber boot. Slide the rubber boot forward, off the terminal and you will fit the red clip here.
Ensure your charger / conditioner is on the 12V setting. and switch on. There is plenty enough "give" in the boot edge seal so that the charger itself remains outside the car, with the charging leads passing over the seal with the boot lid closed.
As an aside, the usual 2 x battery conditioner's used by enthusiasts are:
The CTEK MXS 5 or the Ring Automotive RA-RSC 612, both of which are suitable for 5.0 litre engines like yours. My preference is the Ring Automotive, because its LCD screen provides ongoing information on the state of your battery and it has more features. Plus the Ring Automotive unit can be switched to cater for AGM batteries - as used in Stop - Start engine systems.
Please note, the battery in your car should be considered as a "Consumable" and you should be looking to change / replace when it gets to 5 years old. The car is extremely sensitive to battery condition, with a failing battery able to throw up numerous random / false dash light and messages. The battery's ability to start the car is no longer the best pointer to its condition.
Enjoy.
N6 JMX