Different Voltage Battery Backup Circuit
Your circuit looks fine to me !

The diodes are a bit over specified though, the 1N5406 can handle 3 A, in your
case 1 A should suffice (the LM7805 is not going to pull more than 1 A).
So you could use 1N4001 instead. But if you have the 1N5406 lying around, you can
use those, it will work just as well.

Just build it and enjoy :-)