FiiO K7 Full Balanced HiFi DAC Headphone Amplifier AK4493S*2, XMOS XU208 PCM384kHz DSD256,USB/Optical/Coaxial/RCA Inputs, 6.35mm/4.4mm Output -K7 does not have a battery, it is powered by a built-in linear power supply, you can purchase an OTG cable to connect to an Android phone, an iPhone or a player. Android phone K7 input setting: K7 [INPUT] switch to USB gear K7 output setting: switch to the corresponding output port according to the interface used, switch to [PO] on the front panel headphone out, switch to [PRE] or [LO] on the rear panel line-out. Connect the phone and K7 via USB C to USB B data cable (such as FiiO LD-TC1) [Note] If there is no sound after you connect, you need to pay attention to the following points: Mobile phone playback software settings, if there is a USB output setting that needs to be turned on, some devices only have sound when the USB output is turned off; Confirm that USB debugging is enabled in the developer mode of the mobile phone; You need to turn on USB debugging on the mobile phone, turn on "Developer Options", and then turn on the "USB debugging" or "OTG" function; Confirm that the adapter cable supports the OTG function, and whether the direction of the cable is reversed; IPhone/iPad You need to purchase a Lightning to USB B data cable which supports OTG function(e.g. FiiO LD-LT1) to connect K7 and iPhone/iPad/iPod, and you can enjoy high-quality music by playing songs.