Settings of xbee sleeping node lost after 2 days of powered off

Have you expereince the same?
How long can you power off the device without suffering the lost of the settings?
After a couple of days I need to reset the settings with X-CTU. Is this normal?

Be sure you are writing the settings to non-volatile memory. If you are writing the settings with the modem configuration tab in X-CTU you are already doing this. If you are using the Terminal tab you would need to send an ATWR command to write the settings.
If the settings are being written and are still lost then you likely have a bad XBee and should call up Digi technical support.