Are you sure you want the MP to restart as soon as power is restored? Have you ever noticed how often power restoration is on and off, sometimes several times, before it finally stabilizes? Commercial and military backup systems whether they are battery, generator, or a combination of both impose a 3 to 5 minute delay before switching back to line power to be sure the restored power is stable.
In your case you have already exhausted the UPS battery to a very low level so it may or may not provide any support during the period of instability as line power is restored. Therefore your immediate boot could be interrupted by a subsequent loss of power and I am ignoring the probability of huge spikes that might get past the filters in the UPS.
