Audi starting problem

I have a 2006 Audi a6 3.2 v6 Quattro...its been
running perfect!!!..untill I was trying to leave after
work. Car started, ran about 5 mins everything
working fine...then interior lights(speedometer,
door handles etc.) Shut off..just pitch black...then
my heater shut off after that my mmi display went
black ...now my car just shut off. I removed key let
it sit for a few mins turn the keys it starts clicking
but wont start. My headlights and interior lights are
working now at this point. I try again still just
clicking noises then my head lights start flickering
mmi display wont turn on cant till up window. Had
battery replaced last week BRAND NEE when I go
into my car settings under battery % its under
50%... Now my car won't even try and turn over and
i can't use my key to lock/unlock/panic alarm it??
Please help oh and when parked/ and or on flat
surface my gas mileage remaining reads 0 and
states im out of gas but I know im not!!