My situation is similar, I don't use the car from October to March and also SORN it so no opportunity to drive either. I have a solar charger from halfords that I plug in to the OBD diagnostic port (XC40) as the front 12V shuts down when with ignition.
Periodically I will run the engine at idle and get everything warm and also charge with a mains charger a couple of times , usually mid-term end of Feb. It has worked so far.
https://www.halfords.com/motoring/ba...0w-496278.html