[Al Skierkiewicz]

Bud,
I think you are getting closer. I would make the input cap 500mfd and add a fuse or breaker to the input side. The diodes will have a 0.6 volt drop if you use standard 1n4xxx diodes. Since the output cap is very small the diode across the regulator is not needed but wouldn't hurt. It might be a good idea to make the diode in series with the backup a Schottky to gain an additional 0.2 volts of available power supply. If you add a diode in series with the charging reistor then the series resistor to the load is not needed. That way the diode in series with the battery will only conduct when the regulator drops out or goes below about 6.8 volts.