Help d3 2.7tdv6 died on idle and wont start!

Morning guys yesterday was out in my landy came home sat idling in car park and died. I've had it started for all of 2 secs and dies. I charged battery all night tried this morning nothing then low voltage on cd head unit came up! Starter spins etc I do have some codes. My key did stop working for the doors a month or so go