Fastrack - effect of low input voltage?

Is it safe to run a Fastrack direct from a battery?

In particular, how will the Fastrack behave as the battery discharges, and the voltage drops below its 5.5V minimum operational input?

Is it necessary to provide external undervoltage protection?

The user manual just says that operation is not guaranteed - but it doesn’t say if the unit might be corrupted, or suchlike…