Flickering Multivision Screen - 12V Battery Issue?

So I knew my 12V was dying, and when it does this my lil multivision screen flickers (the one that displays if you're using petrol or HV battery etc), until you run the car for about 5min then presumably the 12V recharges enough for the screen to hold steady. I recently got a brand new 12V battery, however, to my horror the multivision is still flickering for the first 5min or so then holds steady, just like before.

Has anyone had this before? I wonder if I need to take it back and try a different 12V battery? Unfortunately there's a bracket in the boot that limits the size of battery I can put in there. I bought this one: ENDURANT CAR BATTERY NS40ZLPP - Battery Warehouse which is 330 CCA. I know it's technically supposed to have this AGM battery: https://www.centurybatteries.co.nz/products/s46b24r however it's over twice the price and 5 less CCA, not sure if that would have any effect over interior electrics like the multivision?

Any help appreciated
Cheers