said by danclan: ... The only time I would expect the cellular backup to kick in would be ~6-8hrs after a power loss and drain of the batter backup ...
According to the Uplink literature, the device monitors phone line voltage when in the "on hook" state, and phone line voltage
and current in the "off hook" state. The latter corresponds to making a call. In the situation in question, the Uplink could
possibly notice that while the voltage exists, the zero current state (i.e., cut fiber) is an error condition.
This is pure speculation on my part, but that's all I have to go on just now.