All is well with the world, the new battery has fixed my problems and the car starts on the button, quick scan and my errors have gone, no battery warning lights or anything.
I find it mental that a battery can cause so much havoc with the cars internal systems, it's just plain weird how it affected everything from internal lights to MMI, tyre pressure sensors and so on.
Anyway, I wanted to wait a few days to make sure before saying thanks to all for your help in solving this, much appreciated!
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