NAS and backup power

Just cutting off the power is not sufficient to test an UPS. Generally, Network Attached Storage receives the messages from its UPS unit constantly and reacts at once. It should be noted that during the start up the notifications about power problems are not received. Additionally, one should take into account that the entire cycle (start up then shut down) may require several minutes.
 Consider the following situation:

1. power failure happens
2. NAS takes power from the UPS battery for some time and then shuts down
3. the grid power turns on and the Network Attached Storage powers up and begins to start up
4. here power is off again.

Now NAS cannot process a report about power failure event until it properly starts up. Once NAS loads, it finds out that the power failure has happened and commands to shut down. Further it may happen that UPS is not able to provide power long enough (to shut down NAS correctly) for the battery is already exhausted during the first cycle.
 One can avoid this by setting the NAS up so that it shuts down as soon as it gets a message that power failure happens.

 All this allows saving battery charge to do one more cycle.

 Alternatively you can try to set Network Attached Storage up in such a way that it does not power up automatically, but per operator's command after the power failure has happened.