If you play music at moderate volume levels, the battery in your Beoplay E8 Sport can support up to 7 hours of playtime. A fully charged case provides up to 3.5 additional earphone charges. With these 3.5 extra charges, you will have up to 4.5 charges (including the first charge) and the equivalent of up to 30 hours of playtime when on-the-go.
In general, the battery life depends on the volume, intensity of music and equalizer settings. This means that the battery drains faster at the higher volume when playing higher intensity music like rock or heavy metal.