I split my year between 2 continents which means that my car is out of commission 6 months of the year.
With my 2012 XC60 T6 I used to disconnect the battery with the following procedure:

• Lock car using key fob to ensure all doors locked
• Unlock driver's door using detachable key blade
• Open bonnet/hood
• Disconnect battery negative terminal
• Close bonnet/hood
• Lock driver's door with detachable key blade

This ensures that the battery does not discharge over 6 months. In fact I was locked out of WA for 2 years during COVID and the car started first time on my return without any harm to the battery.

Now I have the vastly improved 2020 XC60 T5 (AU Momentum) which brings so much more sophistication but adds some complexity for disconnecting the battery.
Can anyone help with the following:

• I have found a 12V battery underneath the rear luggage area. Is this the only battery or do I have another service/starter battery elsewhere? I think I may have another 48V "service" battery in the engine compartment.
• I can unlock the left hand door (for me this is the passenger door) using the detachable key blade but this sets off the alarm. The owner's manual suggests that this should be deactivated manually but I haven't found out how to do this. Elsewhere in the 'alarm' section of the manual it states that the alarm cannot be disabled. Can anyone tell me how to deactivate the alarm manually?
• Assuming I can deactivate the alarm, I can then open the boot/trunk and disconnect the battery terminal.
• Alternatively, can I just lock all the doors electronically then open the boot/trunk and disconnect the battery terminal without worrying about unlocking any of the doors? Previously I needed to open the door to open the bonnet/hood.
• Can I close and lock the rear tailgate without battery power, and if I do how can I re-open it?

To preempt those who might suggest using a trickle charger, my car is garaged in the basement of an apartment block without any resident access to a electric supply.

 

If your car has stop/start you will have a small 12v battery under the hood that should be disconnected also. The later B5/6 cars have the extra 48 volt battery for the ISG (integrated starter generator)