Your request is challenging. There are home systems which are plugged in and tend not to be rechargeable. There are portable systems that are rechargeable but tend to have very limited inputs - usually bluetooth and/or AirPlay. Additionally, most of these units do not have a USB input. The SRS-X88 is discontinued and current devices don't have that input as many support DLNA & WIFI which allows for streaming files above 16/44.1. None of those units are rechargeable though.

Bluetooth aptX and AirPlay support up to 16/44.1 so if your FLAC files are not above redbook resolution you should be fine streaming to one of the nicer portable devices. If your FLAC files are Hi-Res (above redbook), I think you may be out of luck.