It sure is cold at the moment but there’s a notable difference between 5°C and less than approx 0°C. The stop/start system recognises this (as my car does), hence the reason for my posts.
The OP mentioned that stop/start wasn’t functioning as it should be and had only worked once since he had the car. That’s why I recommended trickle charging the battery overnight or alternatively by taking the car on a few long journeys. It’s also why I provided the Jaguar detailed info on stop/start which shows the conditions that will prevent an automatic engine stop (including if the external temperature is less than approximately 0°C and if the climate control system demand requires the engine to be running e.g. in defrost mode).
Thanks for your final comment......your posts are also excellent