It's certainly a good idea to have some kind of back-up plan. Battery powered and water powered pumps each have their own advantages and disadvantages. The disadvantage to the battery system is that it has a finite capacity because the battery has a finite capacity. You can use a bigger battery or multiple batteries but there's still a finite limit. There is also an ongoing maintenance cost because the battery needs to be replaced at regular intervals. The advantage is that it's completely independent and there's no operating cost (beyond the cost of recharging the battery). Water power pumps will operate, in theory, indefinitely but their performance and efficiency is directly related to city water pressure. The greater the city water pressure, the more water the pump can remove. If you have very low city water pressure, it may not be able to remove enough water to keep your basement dry. The drawback is there is an operating cost in terms of water required to operate the pump, which is difficult to calculate because you don't know how long the power will be be out or how much water the pump will be required to remove. If a major catastrophe occurs and you loose city water pressure (or experience a significant decrease in city water pressure) you could be in trouble. The choice is a matter of personal preference, comfort level, and a bit of speculation as to what your worst case scenario might be.

I've only been a member for a few years now. Mostly I stay in the lawnmower and lawn forums. I came across this while at work the other day and just wanted to share since there has been a few posts recently about back-up systems. I can see why some places may not like them but according to the manufacturer it uses one gallon of city water to move 2 gallons of pit water.

"What is a radon mitigation system ?" An inline blower and a vent to the outside from under the slab. Any radon is removed from under the slab and vented to the exterior. I would test before bothering with a mitigation system.

The short answer, I think, is no. Even a small sump pump pulls something like 6 amps (720 watts) so you'd need a pretty large UPS to keep on running for any period of time. From APC's runtime chart a 1500 VA back-up (retail $250) would keep 700 amps running for 5 minutes. Motors have a fairly large in-rush of current on start-up too. I don't know if a UPS is designed to handle that. The pumps sold with battery back-up systems are 12 volts DC, so you couldn't just plug one into a UPS either. It is probably far more cost effective just to buy a automated battery backup sump pump system.