Replaced v12 battery dash lights went off again

2005 model. For two months I’ve consistently had to unplug the v12 battery to reset so that the dash lights work. 1 week ago I was driving and the red triangle of death along with ‘Problem’ on display screen and a bubble looking icon with exclamation mark down the middle of it came on. Car died 2 miles later. The v12 battery was very hot as I had never heard the cooling fan try so hard to cool the heat of the battery down. Replaced the v12 battery. A day later the dash lights are now out again. Any ideas?