Many auto parts stores offer a free comprehensive electrical test of starter draw, charging voltage/ripple & ign-off draw if they can spare someone at the counter. Some will give a printout of the results.
The battery is generally out-of-sight. out-of-mind on these. Although it is a maintenance-free battery, terminals & posts can corrode. Some corrosion may be between the post & terminal and hidden from view. Take both terminals off and clean them.
A battery may check OK as soon as you turn off the car. Sit and play the radio a few minutes before having the test. This will remove the surface charge and allow a valid battery test.
Measure radio draw, perhaps it has an internal problem? It shouldn't draw more than 1 amp turned on.
Batteries can go bad at anytime. If the caps are removable, test the electrolyte specific gravities. One cell may be having an issue?