The R-4 will
NOT switch to the internal AA's if the power being supplied through the AC adapter input dies or is removed.
From the R-4 manual... "If you disconnect or reconnect the AC adaptor, the power will turn off even if batteries are installed. Please turn off
the power on the R-4 itself before you change between AC adaptor power and battery power."
The R-4 PRO
WILL keep running and swtich to the internal AA's.
The R-4 PRO manual says... "If there are batteries in the unit while an AC adaptor is being used, normal operation will continue should the line
voltage be interrupted (power blackout or power cord disconnection)."
I have the R-4, non-pro, and have not had it be an issue... but it is something to be aware of... if your dvd battery is dying, remember to turn the unit off before removing the power. You can then turn it back on and it will use the internal AA's.
cool stuff