MAJOR DRAWBACK - Kalenji ONRHYTHM 110 CHEAP HEART RATE WATCH - UNBOXING AND REVIEW - DECATHLON

UPDATE ON THE CONNECTION PROBLEM:
It seems to work outside just fine, although still not very fast, but in buildings it is completely unreliable. It might be the signal reflections off the walls or the WiFi Networks around, but it barely transmits any heart rate data and the connection breaks down all the time. For me, this means I can forget it on the elliptical at home.
The major problem of the Kalenji ONRYTHM 110: The connection of the heart rate sensor strap is not very stable, even with full new battery. In fact, I had to begin by changing the battery in the chest strap, because it barely worked with the factory battery. After changing it, it connected most of the time, but the connection was not very stable and therefore the measurement not very reliable.
What do you think about it?