Little update. So I fitted the new battery (as MJ's suggestion). Good voltage, car fired on the button, idled for a bit. Checked voltage 11.8V. so not charging. Connections good. Car back to idling like a pig, battery warning light on, EML flashing - car dead.
Physical inspection - Alternator has pooped itself, spins both ways so looks to be the same issue Ronin had a while back. So that is going to a WIP.
I am just hoping I have not stuffed the fuel pump, although on the key turn with the good battery I still hearing it 'doing its thing' so thats good eh?