Discussion
It is impossible to prevent the destruction of data when power is turned off while data is being saved.
Examples of measures to take for back-up data which has been destroyed are:
When initializing the saved data, an initialization finish flag (or dirty bit) should not be written until after the initialization is completed. Push the Reset Switch during the initialization process to make sure that no abnormalities occur during subsequent initialization attempts.
Discussion
A specific value is stored in back-up memory when it is shipped from the factory. However, this value may be lost over time.
Discussion
Each EEPROM address 0~63 can normally be over-written around 100,000 times. Beyond this point, memory cell deterioration may prevent data from being written normally. Data can safely be stored on a EEPROM for up to ten years. However, if no new data have been written, the memory cells' charge gradually dies and data may not be readable beyond this period. Thus, it is important to include check sum and parity bit data in order to check data reliability.
For more information, please refer to Developer News 1.4: EEPROM (Electrical Erasable Programmable ROM).