Parking heater only with second battery
Horor vision: a frosty morning on a lonely highway resting place. The SLI battery is empty, because the parking heater worked to long. The solution: a second battery.
A decrepit SLI battery can be weakend by a small effort, that staring the ICE is impossible. Special when it's very cold.
At sleeping in the car and using the parking heater in the morning, it should be certain that it's possible to start the engine half a hour later. But not only the parking heater can drain the SLI battery. Charging 100 Wh notebook batteries, work 5 hours with the notebook, use the car radio. Makes all together 20 Ah. Sounds not so much. But my experience shows, that half an hour drain 1,5 A can make an old 95Ah SLI battery unable to start.
At all examined minivans, only VW Sharan and Seat Alhambra has a second battery ready to order.