This just happened to me too. I had the state emission inspection done, and the next day when I went to drive the car, I got the "Battery low - please start ignition" warning. This happened once before too, and I had to jump start the car to drive it to the dealership. They swear they don't know what the problem is, but sounds like I just need to be aware of this going forward anytime I have any maintenance done, since there doesn't seem to be a fix from Jaguar.

 

Ya, a quick disconnect of the battery does the trick.

 

Reviving an old thread....
Did you ever find out if the start/stop battery also needs to be disconnected on the 2015 along with main battery for OBD drain issue?

 

No need to disconnect the aux/small battery at all, just disconnect the main battery.