Boombox Power Circuit

A friend is building a boombox like mine, and wanted to know how the battery, charger and stereo were hooked up. Here is a quick circuit diagram explaining how I chose to wire the stereo. 

 The the switch serves two purposes in the circuit, the first is to disconnect the amp from the battery when the stereo is not in use. If this was not done, the Amp would slowly drain the battery, and potentially cause it harm by discharging the battery too far.
The second purpose is to allow the stereo to be hooked up to an external power supply like a large car battery, and have the internal battery disconnected.