Yesssss: it was the wrong Battery Relay PIN!!
))
Yippee: works like a charm now.
One very last question remains: Does the refer to the device's minimum voltage to be operated? And if so, wouldn't it be wise to set the battery driver to a value around or even to avoid "deep-sleep-wake-up"-issues?

Yippee: works like a charm now.
One very last question remains: Does the
min_V:2200
2300
2400
Quote:Device configuration, as extracted from Tuya:
- Button (channel 0) on P20
- Status LED on P26
- PIR sensor on P16
- Battery Relay on P17
- Battery Max Voltage: 3000
- Battery Min Voltage: 2200
- Battery ADC on P23
Device seems to use Battery Driver. See more details here: https://www.elektroda.com/rtvforum/topic3959103.html
Device seems to be using CBU module, which is using BK7231N.
And the Tuya section starts at UNCOMMON POSITION 0