ZAGG Boost Plus - Manual (Page 5)

4.2 Volume Control
To adjust the volume simply change the volume level on your mobile device and the
Boost automatically adjusts the output volume.
4.3 Audio in Operation
The 3.5mm jack is for optional wired audio input for most mobile devices.
5. POWER
The speaker can be powered by three AA batteries or external DC in from the
Micro USB socket.
When the batteries are first inserted, the speaker will stay in its default
Standby Mode.