We always suggest that the electrician install a UPS unit for our Vantage controllers.
It's not so much to keep the power on, as it is to use it as a secondary defense against the utility company power surging, and the controller failing.
We have many instances where the power goes back on, kicks off, goes on, kicks off, etc., and the controller fries.
Yes there is built in protection, but you can only kick the equipment so many times.
Its inexpensive protection.