How can it be that the battery condition has already dropped relatively sharply after a short time?

The battery consumption depends on the set transmission interval. The smaller the transmission interval, the greater the battery consumption. It also depends on how often the Smart radiator valve has to regulate. In places such as the basement, where the temperature drops relatively quickly, the actuator must regulate more often.
Since several installation runs are carried out during initial commissioning, the battery is loaded more than normal; during normal operation, the battery consumption levels off again.