bought a high mileage passat gte - so questions

[roadwarrior]

Just bought a 2020 gte est, so now we have a 2014 tdi, a 2017 190 tdi and 2020 gte petrol, a bit of a theme going here methinks.

so its sort out the wrangles time, the 2020 has a tailgate that unlocks but does not move and needs to be lifted about a foot and then it lifts itself - is that tired struts ? is it intended to open itself and swing up from unlock or not ? my 190 saloon swings up when i use the middle button on the remote. but my wifes 2013 estate merely unlocks but with a tad more enthusiasm than the gte tailgate.

I am struggling a little about the battery charging, i have a 3 pin plug charger which is fine and good enough for me, but reading im told i need to keep it between 30-80% charged but there is nothing to tell me state of charge - it just tells me charge in miles and then charges to 100%
and then the amazing battery under the bonnet with huge cables coming of it - is that my only battery or is there another battery somewhere that powers the central locking / ignition ect, and what does the type 2 charger actually charge, is it possible if i only have one battery i would be locked out of the car and no way of charging as the charger will also be locked as it needs power to open ?