When the rain gets torrential our sump pump also goes off as often as every 4 minutes. When it is light it goes off anywhere from every 15 minutes to every 45 minutes depending on how soaked the ground has already been. Even after the rain totally stops it may keep on pumping every hour or two until the ground has dried out.
Several years ago we had a company called B-Dry come in and put in some special wall covering and I think some sort of pipes behind that and then they put in a big cistern in one corner of the basement. The sump pump sits in the cistern and when that fills to a certain point it pumps up and out through a pipe that runs outside, is buried in the lawn, and then empties way away from the house. The basement used to flood badly. Now only if there is very prolonged torrential rains do we get very slight, minor seepage in the two other corners of the basement not covered by the system.
I was always really anxious about what would happen should it be raining hard and the power went out so that it no longer was running the sump pump. Three years ago I got a very expensive big battery system for it. During that awful storm a couple of years ago the power of course was out and the battery kicked in and worked for 30 minutes and that was it, it died. Depending on the number of times the pump had to run it should have lasted anywhere from 10-24 hours. Even if it had lasted it wouldn't have done the trick for the duration of the storm and power loss. So, I was downstairs manually bailing water. During the worst of the storm I could barely keep up with it. It is an awful memory.
Following that I vowed to get something dependable. I found many other battery systems with similar durations, and I knew that was not what I wanted. I found some with 2 batteries that might last 15 to about 30 hours. I knew that wasn't what I wanted either. I did a lot of research and learned that there are water powered systems that can work well in residential situations. The backup pump is hooked into your incoming water line and the backup pump sits in the cistern just above the electric pump and then somehow (it's very easy but I still don't comprehend it) the water powers the pump if the electricity goes off. I called a local plumber and he recommended it over the battery powered one. I had one installed by them. It rained that weekend and for some reason my electric pump had gotten set so that it was not working, and sure enough all weekend long the water powered one worked until Monday when they came out and set the electric one properly. So I know the water powered one can work just fine for an extended period. I figure that while batteries can die, if the water system is down we have a much bigger problem (a major earthquake?) to worry about than the basement flooding.
Oh, and those of you who have electric pumps running often, did you know that they can fail after about 5 years and should therefore be replaced every 5 years? Our failed right around 6 or 7 years and that is how we learned about that.
So now I am much less stressed when we get these big storms.