Backup power can be used when the main power is not supplied to keep RTC running and navigation
data. For a short term VCC off, with this backup power, the GPS module is capable of a faster TTFF,
shorter Time-to-First-Fix, and short hot start time at next power on.
For most system, it is recommended to provide the module with backup power (e.g. Li-Ion
rechargeable coin battery, super cap) See figure for reference design.