I’ve noticed (and Soudcore support confirmed) that this was because I’ve spent a considerable amount of time using the earbuds for calling using my pc. Since this also uses the microphone, the battery consumption is far more (around 40% more) than the music playtime. So that’s it for me so far.
This is what they told me for testing correctly.
Please fully charge the earbuds and test the playtime again at an average volume. Please also try to switch the main earbuds and then do the test again to see if the problem persists.
By switching the main earbuds, what I mean is as the earbuds support Master/Slave switch, both of them can pair to your phone as a master device. When the right earbud is master, the Bluetooth name is Liberty Air 2, when the left earbud is master the Bluetooth name is Liberty Air 2-L, you can choose to connect the other side and then try to use them again to see if the same problem persists.