The charging circuit is broken, if possible, change a charging IC.
(You can also string a diode from the USB positive terminal to the battery positive terminal, so you can plug it into the mobile phone charging head or computer USB use, but you can also install the battery to charge the battery, provided that the battery has a protection board, but this charge will not turn the light) Use the battery directly connected to the stereo use, and then lead to two wires with universal charge to charge the battery! Connect a 5V adapter directly to the place where the battery is connected, or use the charger of the mobile phone. After connecting 5V, the battery can not be used in parallel (5V charging voltage for the battery is too high).
(This circuit of the general audio can work at 5V voltage, but it is best not to exceed 5.5V) Hope to solve your problem.