Have you recently had a state inspection done, or codes read? There is an issue with the OBD port that will drain the battery, if the connection is not properly closed before unplugging. A key to watch for is the triangular hazard switch light. It will remain lit after shutting down. Normal behavior is for it to go out ~10 minutes after shutdown. The fix is to disconnect the battery ground cable for ~30 seconds and reconnect. Be aware you’ll need to reset power windows, per owner’s manual afterwards.
Thanks so much. That was really helpful, especially the description about the hazard light issue. As instructed, I disconnected the ground and after a minute and then reconnected. However, no change to the circumstances. I did talk with a Jag dealer service rep who did inform me that they do a hard reboot after each OBD hookup. They don't know why the battery goes dead but it does. So, I jumped it with my other car and it wouldn't start. Turns out, even with the other car operating with higher revs it wouldn't start. So, I had a service with a battery pack jump it and she fired up. So far so good but I'll know better tomorrow when I try it again. Windows were unaffected, but of course the clock and date are off which is no big deal. To sum up, your recommendation would have worked but the battery was drained. I guess next time I get it inspected (NYS requires hook up and analysis thru the OBD) I'll have a hard reboot done as well. English electronics eh?
One other issue I noticed. The stop/start feature has been inconsistently working recently, and when I put some battery charge driving after the jump I noticed it wasn't working. Don't know if that is related to the inspection/OBD generated issue or if it's a separate issue, as in the Ni Cad battery for that feature is now kaput. Note: the stop/start light on the switch is still illuminating.