Sonar dropping out

Hi Guys, my ping 360 works fine, except for the dropout which sometimes can happen in ten minutes, or sometimes as short as two or three minutes. Restarting Pingviewer shows message ’ No devices detected’. I tried manual connection, every combination available, still no go. I can get the display on screen but no scanning. The only way to get it up and running again is to disconnect and reconnect the sub battery.
Any ideas / guidance ?