Storms take the power out and fill the pit in the same hour. A backup is not an accessory — it is the half of the system that works when the other half cannot.
The worst night your sump pit will ever have is the night the grid goes down. That is not bad luck; it is the same weather. Wind and saturated ground bring down lines, and the same storm puts a season's worth of water against your foundation in six hours. A primary pump with no electricity does nothing at all.
There are three honest answers to that, and they fail in different ways. A battery backup runs for a measured number of hours and then stops. A water-powered backup runs indefinitely but needs municipal water pressure and spends a lot of fresh water doing it. A generator keeps the primary pump running at full capacity but requires somebody to be home, awake, and willing to go outside.
Which one is right depends almost entirely on how long your outages last and whether you are home for them. Start with water-powered vs battery if you have city water, or battery backup vs generator if you do not.
The storm that fills your pit is the storm that takes the power out. This is the half of the system that works when the other half cannot.
Top pick: Wayne ESP25N battery backup system
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One box, two pumps, floats already set at the right heights. It removes the mistake that disables most home-built backup installations.
Top pick: Basement Watchdog Big Combo
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No battery, no charger, no runtime limit. In the houses where it fits, this is the most reliable backup you can install.
Top pick: Liberty Pumps SumpJet SJ10A
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Your backup system is only as good as the battery behind it, and the battery is the part everyone forgets until the night it matters.
Top pick: Universal Power Group UB121000 (12 V 100 Ah AGM)
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A generator is the only backup that gives you the primary pump's full flow. It is also the only one that needs a person standing in the rain.
Top pick: Westinghouse iGen2600 inverter generator
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A backup that fails silently is not a backup. Connected monitoring is the cheapest way to find out while you can still do something.
Top pick: PumpSpy sump pump monitor
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One has no runtime limit and four conditions attached. The other works anywhere and runs out. That is the whole decision.
Top pick: Liberty Pumps SumpJet SJ10A
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One works while you sleep at reduced flow. The other gives full flow but needs you awake and outside. They are not really competing.
Top pick: Wayne ESP25N battery backup system
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Work out your worst realistic outage first. Not the average one — the worst. Then pick the system that covers it with margin.
A 12-volt battery backup is the most common choice because it works in every house, needs no plumbing, and installs beside the existing pump. The trade is runtime. Most systems with a single group-27 AGM battery will run somewhere between 5 and 12 hours of intermittent cycling, depending on how often the pit refills. Continuous pumping drains it far faster. The honest way to read a runtime claim is as a cycle count, not as hours — see how long a sump pump battery lasts.
A water-powered backup uses the pressure in your municipal supply to drive an ejector that lifts sump water out. It has no battery to age, no charger to fail, and no runtime limit at all. In exchange it needs a well-pressurized city supply (it does nothing on a private well, because your well pump is also out), it uses roughly one to two gallons of fresh water for every gallon it removes, and many jurisdictions require a backflow preventer on the connection. Where it fits, it is the most reliable thing you can install.
A 2,000-2,600 watt inverter generator will run a 1/3 or 1/2 HP sump pump comfortably, including its starting surge. That gets you the primary pump's full flow rather than a backup's reduced flow. The catch is operational, not technical: somebody has to be there to start it, fuel it, and keep it outside and far from windows. It is a good second layer and a poor only layer.
A combination unit ships a primary pump and a battery backup pre-matched in one package, usually with a single pit lid and one float assembly. It costs less than buying both separately and removes the most common installation mistake, which is setting the backup float too low so that it never gets a chance to run. The trade is flexibility: you are buying both halves from one manufacturer. See combination sump pumps.
Think in cycles rather than hours. A typical group-27 AGM battery supports somewhere in the region of 1,500 to 2,500 gallons of pumping before it is flat. In light inflow that can be a day or more; during continuous heavy inflow it can be under six hours.
You can, and it will work briefly, but a starting battery is designed for a short high-current burst and is damaged by the deep discharge a backup run demands. A deep-cycle AGM battery will survive many more outages and does not need topping up with water.
No. Your well pump runs on the same electricity that just failed, so there is no pressure to drive the ejector. Water-powered backups are a municipal-supply solution only.
Yes. Mount the backup's intake and float above the primary's switch-on level so the primary handles normal duty and the backup only starts when the primary cannot keep up or has stopped. A backup mounted level with the primary runs constantly and flattens its battery for no reason.