FP,

The only thing that comes to mind is to either pull the radio out and unplug it's harness for a few minutes or disconnect the battery for a few minutes. When you re-connect battery or radio, TRY to make it a quick, "clean" reconnection, not a shaky "connect-disconnect-connect" affair that can confuse the microprocessor in the radio.

Maybe when you changed the battery, you made-and-broke the connection a few times and confused the micro-P.

Were either of the radio fuses blown? If so, that does not sound encouraging.