I had to replace my battery in my 2016 LR Discovery in Oct 2018. I starting getting the same message again the past two weeks It would usually happen when I got in the car on short hauls. Then, I notice my rear door would not operate correctly so I took it to NTB where I bought the battery. They said it was fine but take the car to the dealer. Turns on that the battery was being drained and the braking module system had not been reset when the new battery was installed. LR service re-charged the batter and reset the BMS systems. LR told me that other places/shops probably dont have tools equipment to do this reset so you might as well just by the battery from LR anyway.
Not sure why you bought a battery since there is a 4 year warranty from Land Rover