Sorry, I am a dumbass and know very little about this stuff, however needs must! I can see the two terminals but everything else is covered by trim. I can get to the positive terminal easily enough, and there is a metal loop on the left of the boot (I think for strapping luggage down??) can I use this for the negative?
Brand new battery going dead is a parasitic drain somewhere. One of the ways to check is if you have a little test light. You would have to go through all the fuses and check after all the ancillaries have switched off (usually 4 mins after having opened one of the doors).
If one of your fuses is lighting up that light, check in your manual which fuse it is. A bad relay could also cause the battery to drain but you would need a scan tool to figure out which one.