There are several options, and I think it depends on your situation. For example - are you on a well or do you have city water?

We went with a generator for part of the house because we are on a well. The generator covers the Geothermal system, well, sumps, and other key areas along with a small handful of things. We are also in a rural area and losing power is not uncommon.

In a new house foundation waterproofing and a well designed gravity foundation drain should make a sump pump unnecessary unless you are in a flood zone. In that case the pump should be powered automatically by a generator.

The battery backup is installed on top of your regular sump pump. Problem is that even with 2 marine batteries, it can only go for about a day. Our basement flooded when the power was out for 3 days and it kept raining. You can use a portable generator but that involves snaking extension cords from the outside through the first floor into the basement to the sump pump.

We took advantage of the flood to empty out our basement storage and finish the basement, and installed an automatic stand-by generator that is hooked up to the natural gas line. It's great for peace of mind since our sump pump ran every 15 seconds during Hurricane Sandy. Automatic standby generators may cost about $6000 up installed. If you don't have natural gas to your house or close by the price at least doubles because you'd have to install a propane tank.

A cheaper alternative is to have an electrician add an automatic transfer switch with a generator subpanel in your garage which has the sump pump and other necessities on it. Then you can use a portable generator and just run it to the subpanel rather than all through your house. I believe this would cost $500 plus the cost of the generator. You'd have to manually hook it up and add gas to it through canisters.

Best bet is a stand-by generator in the garage, wired to a sub-panel. Fuel can be natural gas (if you have it), propane, or gasoline. Controls can range from manual (you start the generator manually and then manually trip the appropriate breaker in the sub-panel) to automatic (everything starts when/if power goes off). $$$ vary with choices.

Ensuring positive exterior drainage away from the house is the first place to start. Good luck!

Thank you all very much for your helpful responses!

It is public water, and gas heat. I will look into a generator when we finish the basement. Until that time would a battery one be worth it?

We didn't have rain constantly for those 5 days, so if it had worked a full day or two, then I think we would have been okay.

The (new) foundation had a membrane system installed to help with water. The current one has no membrane, and the drain all along the walls was sealed for the radon system to work.

I'm sure the poster above didn't mean a generator in the garage in the usual sense. It has to be in open air or at least right at the entrance of the garage to prevent carbon monoxide poisoning (think of a gas powered lawn mower in the garage) . The subpanel should be in the garage.

The electrical backup is needed regardless because it will buy you the minutes/hours needed to setup or troubleshoots a generator.You may be sleeping or not home when the power goes out.

Yes, you are very correct: a garage-based generator needs it's own exhaust vent or door that can be opened when the generator is in use. I just overlooked the obvious. Thanks for the important correction!

Putting the generator in the garage eliminates the need for weather protection. Placing the generator outdoors means a weather-protected system.

Yes to the battery back up for the sump pump. But if your builder is installing it, make sure he doesn't cheap out on it. I lived in a house with a low end back up battery sump pump and it had a feature that caused it to beep intermittently to let you know the battery discharging. Sounds like a great idea . . . until you are trying to sleep. And there was no way to turn off the beeping.