Short lifespan...
It seems that the life of this battery is shorter than expected...
The original battery was indicated to be changed (inverter self-test) after 2 years and 4 months, which I did.
After 2 years and 8 months, same diagnosis!
However, the inverter is only subject to a few mains problems (2 or 3 times a year).
The lifespan still seems a bit short to me, even though the manufacturer indicates a lifespan of 3 to 5 years!