A6 C6 4.2 Battery Issue
 

Hey guys i have a 2006 Audi A6 C6 4.2 every now and then when i get home from wherever and later on try to unlock or start the car none of the dash lights come on, i then have to go to the trunk, disconnect the battery then reconnect for the car to start or work. doesn't do this everyday just one every week or so. what can i do to fix this issue? any help will be greatly appreciated