Z-Wave and Philips hue batterylevels show only 100% or NULL (Openhab3)

Hello Community,

first of all: I’ve googled and also searched here, but I couldn’t find a solution. If one of you finds a link to a topic where this problem has been solved, please post it.
Second: I’m a beginner, so please don’t kill me if it’s kind of a simple thing for you pro’s.

I run a Ubuntu 20.04 system with OpenHAB3 (not openhabian).
Z-Wave Bindings are installed.
Z-wave Controller is the Z-wave.eu Dongle UZB* and included as Thing.
I have several z-wave battery devices such as Popp solar outdoor siren II, and two Abus smoke sensors.
These devices are also included as things and online and the most channels (included as item) are working (switch to turn on siren / status of smokesensor).
The problem is, that the battery levels show only 100% (Siren) or NULL(smoke sensors) and are not changing even if the solar siren runs out of power.

Interesting enough
There are also Philips hue sensors with battery where I discover the same issue. And hue is not a z-wave but a special zigbee standard.

If tried to link an item to the channels as number, as number with dimension (energy, voltage, you name it) even as point and some others. Nothing seems to work.

My conclusion is, that I’ve done something basically wrong as both systems do not show correct values.

It would be great to get a step by step how to.
If you need screenshots or protocols or something please tell me also where I can find for example the protocols. Keep in mind, I’m new to this stuff.
I can help myself a bit with linux shell (ubuntu terminal).

Thanx in advance