Am I best to check both batteries? One under tyre and one in rear quarter? What is the difference?

Hi All, I have a 2015 Range Rover 4.4 SDV8. The centre screen (radio/nav etc) is temperamental. Start vehicle, screen loads up as normal to home page but touch screen does not work. The screen functions as normal (current location changes, heated seats screen pops up when button pressed etc)...