First, thanks for clearing the terminology.
As I was hooking up the battery maintainer I noticed an existing set up to plug in a charger where leads for the a charger were permanently attached to battery terminals. I just followed it. But I am going to change the negative to a ground in the trunk to avoid any chance of foul play. This is how I attache this unit in my Mercedes.
I read that some people attach it in the hood using fuse box connection point. Is it OK to do as this will eliminate any possibility of leaving the trunk light on or crimping/crushing the leads of charger when you close the trunk.

 

The "is it okay" isn't specific.
The car doesn't care if the battery's a traditional flooded or absorbed glass mat - as long as it has about 12.5 volts for it.
It's typical for the earlier few years of the X351 to be overly sensitive on the static battery level. Ours always has popped-up the low battery warning after just a short time of having the door open or running anything electric for a few minutes.
And all of it's systems do have a large power draw compared to most other vehicles.
If you read through related forum posts, you'll see that it's not unusual and something to be aware of.
We've never had our battery die, but I did notice when the warning would be more frequent/annoying then usual that it was time to check the battery and subsequently replaced it (early 2020) - with an Interstate AGM Group H8/49 (it had an AGM when we got it in 2017).
Now if the "is it okay" includes running electrical systems with the car not running, expecting to play the stereo for more than 5 or 10 minutes with it not running, leaving the door open or something like that, I don't think that anyone in the forum has identified a battery that will keep the car's system from telling you to shut it off or start it up.
It's the annoying nature of the car's system that I believe (if you read more posts) was addressed in subsequent model years, likely after complaints.

 

Yes, I was sitting in the car ( off but powered on ) adjusting consumer functions when it flashed "Battery low / Start engine". I will have to learn the limits of my car, since the issue is structural.
Thanks for you input.

 

I attached my CTEK to the battery in the trunk using the alligator clips with the negative pigtail attached to a chassis ground. Those clips are very strong and I've had no problems.

I run the CTEK power cable out of the trunk underneath the trim and close the trunk lid without any problems. I leave the female CTEK connector in the trunk and close it with the included rubber cap. Installing and removing the CTEK is quick and easy.

 

Upon further probing, current battery was found to have been manufactured in Dec 2015. I replaced it with an AGM battery from Wallmart that came with a 4 year replacement warranty.

 

I can tell all of you that from first hand experience, an AGM battery makes all the difference. I just bought a new 2016 battery from a non-Jaguar dealership. It looked like they had just put in a new battery (a non-AGM one). The car seemed to like it initially. But, after about 2 weeks and 1 time leaving the door open for 10 minutes, the battery started giving me grief. I even recharged it and the battery fried itself. Now that I have an AGM in there, all is good again.