As you have discovered, unless there is a non-standard drain on the battery, 2 1/2 weeks is fine to leave the XK for without a maintainer.

I personally only ever use one if I have been doing work on the car or giving it a decent spring clean with all of the doors and boot open otherwise I just lock and leave.

I am heading to Europe for 3 weeks later in the year and will be happy to leave the XKR 'unmaintained'. My Aston is a different story though as it does seem to genuinely have an issue. I had the tracker disabled and disconnected a few weeks ago and that has improved things but, even though the battery is reasonably new, the voltage had dropped to 12.4V after 5 days so I have resigned myself to having to use a maintainer if I won't be driving it for 3 or 4 days.

 

I concur.
A good battery today is quite resilient to “drain” by sitting. Its the “draw” on the good battery that depletes them.
You can reduce the draw. I have posted the specs concerning draw, before.
A bad battery, a different story.

As I keep her in the garage, I do not lock her. The result, she can sit for 6 months without needing a charge. Coincidentally, so can my boat.

 

I charged my one year old AGM battery (880 ccv) to a max of 12.9. Disconnected the battery and let it sit. After 2 weeks, voltage (using a very accurate DVOM) was 12.8
My "storage shed XK8 " doesn't get much use since I bought my 07 XKR. Actually no use. If I leave the battery connected (and locks double clicked), it drains quickly. Disconnected, no problems letting it sit.

 

The "double lock" feature is disabled on North American market models because it disables the inside door handles and prevents a child or anyone else from opening the door and getting out. That's a safety hazard according to the US National Highway Traffic Safety Administration (NHTSA). On North American models, when you press the lock button the second time you will hear a "beep-beep" from the sounder, which is an error message and not a confirmation that your car is double-locked.

In the UK and other markets where it's available, double-locking prevents a thief who breaks the window glass from opening the door with the inside handle.

NHTSA values life more than property.

See:
https://www.jaguarforums.com/forum/x...-alarm-230706/

https://www.jaguarforums.com/forum/x...ocking-234198/

https://www.jaguarforums.com/forum/x...estion-222834/