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Side answer:

The negative connection from the charger needs to be connected to the chassis because (1) it is safer in case of explosive gases near/from the battery (vent tube not connected or broken), (2) it is easier to make this connection for both 12V batteries, (3) a fully dead battery won't act as a total energy sink if you're just trying to get it started/powered up, and (4) the BSM on the negative post of the starter battery needs to observe the current flow through the battery and this won't happen if you connect directly to the starter negative post.

For #2, there's that chassis brace running along the back of the frunk compartment between the shock/suspension towers that makes a good ground point if your charger can attach to it. If you have the side covers pulls loose, you can see where the ground cables attach between the body and the battery. You can use those points too.

For #3, Here's an example of what I mean. I once had a completely dead battery in a Discovery. Attaching jumpers to the posts of the battery would not get it to turn the starter or even shift to neutral. Moving the negative connection to the engine (essentially opposite end of the ground cable) and it started up.

For #4, the BSM is under the plate seen to the left in the first battery picture posted above. You could clamp to there (not the battery post) but you can find other places with more area for the clamp. You won't chance frying the BSM with an electrical arc too.
Thank you for all of your information and advice.
Since we bought our 2019 SE in June 2019 and don't know how long it sat on the lot before that, and
since we are planning to drive from South Carolina to Key Largo in November, and
since we don't want our cat to turn into a brick somewhere on the road in Florida,
we made an appointment at our dealer in Charleston in September to have both 12V batteries replaced.
If they test "bad" Jaguar will pay, I told them if they test "good" replace them anyway and we will pay.
For us, way too much aggravation to have surprises on the road.
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