Hi Nigel, I'm not sure about that specific part number, but I can confirm that the Fiat Bravo back box does fit the Delta as the floor pans are identical.
@ 12v you've got only 25% in it @ 11.8v you are 0% as Nev said flat You can subtract a lot of CCA / voltage at current UK temperatures. I'm a ecumenical about big 800/80 big batteries on 2.8 GV's but the won't fit without moddin the battery tray and a very salty price point. The Optima 'RedTop' Spiracell battery - 12V - 50Ah (815cca) is always a good starter battery. YOU make sure it will fit your car and the terminals are the right way round my friend. A brand new pair of linked £600 each batteries will not stay charged if you don't give them frequent long enough trips. Lifestyle (lack of use) is a big killer [flat/sulphates] of GV batteries. Best of luck.
Tried charging for 12 hours and it went up to 11.9 haha! Was definitely the battery (thank god for Eurocarparts New Year Sale!). New battery in and started right on up! The plonker owner before me had swapped the positive connector side to fit a battery the wrong size in so it was a pain in the ass to put right but once connected all was good Now I'm just hoping for no leaks of the coolant over the next week or so