There are two steps to saving a registration, the second step however is often overlooked. This process has not changed in decades for Yamaha arranger keyboards, regardless of the model.
Step 1: After setting all the information you wish to save on the main page, Press the MEMORY button, then press the registration button you wish to save it in. Be sure, however, to have the boxes ticked in the registration memory contents page that you wish to save.
Step 2: Once you have saved the individual registrations (1 through 8) you must now save the registration bank. Next, press the "J" button in the lower right corner of the display, then select SAVE. This will open the registration bank page. Now, you must name the registration bank in which the registrations are going to be stored. There are provisions for naming the bank at the bottom on the screen. After naming the bank where the registrations are stored, press OK and now there are permanently saved in the User Memory area of the keyboard. If you want to save this to your USB drive, you must tab to the USB1 after pressing the "J" button.
Now, Yamaha has not used a storage battery since the PSR-500 model became available. All the OS and saved user information has been stored on a chip since then, thus no battery needed.
Hope this helps, Tom, and others,
Gary