If you play music at moderate volume levels (at volume step 10 of 32), the battery of your Beolit 17 is fully capable of running for up to 24 hours.
In general, battery life depends on the volume level and intensity of the music. This means that the battery drains faster when you play at high volume levels or you play music with high intensity, such as heavy metal.
Charging your smartphone using the USB connection will significantly decrease the battery life of your Beolit 17. Therefore, it is advisable to remove your smartphone from the USB connection after sufficient charging.