Let's back up. I printed out all of this thread's comments regarding your
radio. It worked and then you saw that it had quit.

You don't mention using an ac wall adapter, so the C cells must momentarily
break connection while the unit is on. Vibration from the speaker, especially
when the volume is turned up, could cause poorly contacting cells to briefly
break connection.

Otherwise, once it is working good, it should continue to work until the
battery dies.

73,
Bill, K5BY