Maximum pressure loss test: here's what we do...
We inflate the ball to the recommended pressure (meaning 0.8 bar).
72 hours later, the ball must not lose more than 15% of its pressure, meaning approx. 0.1 bar. The pressure after 72 hours must, therefore, be at approx. 0.7 bar.
This also means that it is quite normal for a ball to lose pressure after a few days.