The present invention provides a portable and compact battery-powered stereo speaker assembly that incorporates a DC to DC converter, which enables power from the internal stereo speaker assembly battery to charge an interconnected hand-held device, such as a smartphone, through a USB connection, thereby extending the time that the device can be used untethered from the AC power grid. A DC to DC converter enables the charging function can be implemented even if the speaker assembly is not connected to the AC power grid, and even if the battery of the stereo speaker assembly is not fully charged. The stereo speaker assembly also incorporates Bluetooth connectivity, a proprietary open wireless technology standard, developed by Ericsson in 1994, employing frequency-hopping spread spectrum radio transmissions in the ISM band from 2400-2480 MHz.(134)