I have a Mk 1 but I turn of the ignition every time I stop at a known long traffic light (well, at least if it turns red as I approach!). Most of my travel is on short local routes, where I know when to switch off and when not. I never have any bother with battery issues, even though I listen to the radio when parked waiting for my wife (a regular occurrence) and leave the car doors open when washing and polishing the car. My battery is 2 years old (RAC, 5 years guarantee).
I have just come back from dropping my wife at her work. Because car is kept in the garage, I start it, drive out then switch off after 10 seconds while I go to lock the garage door. I then drive her to work, switch off while she gathers her things and until I see her safely into the building, and today (as usual), I got stuck at the 3 minute traffic light. So I switch off there too. I do switch to sidelights while sitting, but I have my blower on (no need for rear demister since car was garaged). That is my Monday to Friday throughout the winter. 3.6 miles at 6 am, then the same to pick her up at lunch time.
I don't know if I am just lucky, or if the low tech of the Mk 1 (no alarm, remote locking driver assist sensors, etc) places much less demand on the battery