A battery-backup sump pump keeps your basement dry when the power goes out, which is exactly when New Hampshire basements flood. New Hampshire doesn’t legally require one, but on the Seacoast we put one on almost every system, because a primary pump with no power is just a paperweight.
The reason is simple. The same storms that fill your sump pit fast are the storms that knock out the grid. So the moment you need the pump most is the moment it has no power to run. A backup pump runs off its own battery and takes over the second the lights go out.
A sump pump only works when it has power
Your main sump pump is an electric appliance. No power, no pumping. That is the single point of failure most homeowners never think about until the basement is already wet.
And in New Hampshire, the power goes out exactly when you can’t afford it to. Climate Central, working from federal Department of Energy outage data, found that 80% of major U.S. power outages from 2000 to 2023 were weather-related, and 23% were caused by winter storms — snow, ice, and freezing rain. The Northeast logged among the most weather-related outages in the country, around 350 events. Those are the same nor’easters and ice storms that overwhelm a sump pit.
The U.S. Energy Information Administration backs this up. In 2021, the average U.S. customer lost power for just over 7 hours; strip out the major storms and that drops to about 2 hours a year. In plain terms: storms are what cause the long outages. The EIA’s more recent data is worse. Interruptions tied to major weather events averaged nearly 9 hours in 2024, more than double the prior ten-year average, pushing total outage time to a decade-high of roughly 11 hours per customer.
A primary pump that sits dead for 9 hours during a March nor’easter is a flooded basement. A backup pump turns that into a non-event.
How primary sump pumps actually fail
A battery backup covers more than just blackouts. A primary sump pump fails in three main ways, and a backup helps with all three.
Power loss
This is the most common one, and the reason this whole post exists. Storm hits, grid drops, primary pump dies, pit fills. Everything above tells the story: in NH, outages and the storms that cause floods arrive together. No backup means no defense for the hours the power is out.
Mechanical failure
Pumps are machines, and machines wear out. The usual culprits we find on a service call:
- A stuck float. The float is the switch that tells the pump to turn on. If it gets hung up on the pit wall or a wire, the pump never fires. A free-moving float is the first thing to check.
- A failed check valve. The check valve sits on the discharge line and keeps pumped water from running back into the pit. If it’s missing or installed backwards, the pump runs and runs without ever clearing the pit. The arrow on the valve should point up, away from the pump.
- A frozen or clogged discharge line. This is a New Hampshire special. The line that carries water outside can freeze solid in January or clog with silt. Water has nowhere to go, so it backs up into the basement.
One note: skip the “pour test” you’ll see online — dumping a few gallons in the pit. It only tells you if a pump won’t turn on. If your pump keeps running, the pit is already full, so adding water proves nothing. Check the float, the check valve, and the discharge line instead.
Getting overwhelmed
Sometimes the pump works perfectly and still loses. During heavy rain, snowmelt, or a high water table, water can pour into the pit faster than a single pump can clear it. A second pump — a backup that kicks in when the water rises past the primary — gives you the extra capacity to keep up.
Battery backup vs. water-powered backup
There are two kinds of backup pump. Here’s the honest comparison for a New Hampshire home.
| Battery backup | Water-powered backup | |
|---|---|---|
| How it runs | Off a deep-cycle battery | Off your home’s municipal water pressure |
| Runtime | Finite — depends on the battery and how hard it cycles | Effectively unlimited while water pressure holds |
| Works in any home? | Yes | No — needs strong municipal water pressure |
| Catch | The battery is a wear item and needs replacing over time | Uses city water during the outage; useless on a well |
For most New Hampshire homes, battery is the right call. A lot of Seacoast and older homes run on private wells or sit on water pressure that a water-powered backup just can’t use — and a water-powered unit draws down city water during the very storm you’re fighting. Battery works regardless, which is why 603 installs battery backups, not water-powered ones.
How 603 sizes and installs a battery backup
The Forever Dry System — our basement waterproofing system — is built around a full-perimeter drainage system, one 1/2 hp sump pump per 120 feet of drainage, a vapor barrier on the walls, and a dehumidifier. The battery backup is the insurance policy on that sump pump.
Installing it right isn’t just bolting on a second pump. We set the backup at the correct height so it takes over before water reaches the floor, run it to its own dedicated battery, put a check valve on its discharge, and give it a clean line out. Then we test it under load — we don’t just plug it in and call it done. Our own crew does the work; 603 self-performs in-house and doesn’t sub it out.
What a backup costs vs. what a flood costs
A battery backup is a small line item next to what it protects you from. We keep the price honest and quote it on the actual job, since the right setup depends on your pit, your primary pump, and your basement. The point is the math underneath it.
FEMA’s own published calculations show that one inch of water can cause about $25,000 of damage to a home (fema.gov). One inch. A finished basement — drywall, flooring, furniture, the boxes you’d hate to lose — runs the bill higher and adds a mold problem on top. The EPA notes that mold can start growing on a wet surface within 24 to 48 hours, and recommends keeping indoor humidity below 60% to control it. A flooded basement blows past that fast.
For context, a full basement waterproofing system is 603’s NH range of $3,000 to $30,000, depending on the size of the basement and the scope of the work. A battery backup is a fraction of that, and a fraction of one flood. It is the cheapest part of staying dry.
The 603 Guarantee on your system
Here’s the straight version, because warranty fine print matters.
The Forever Dry System carries a full transferable lifetime warranty — it can pass to the next homeowner, as long as no other contractor or homeowner has tampered with the work.
Sump pump systems carry a 3-year warranty, and the battery is excluded. That’s normal — a battery is a wear item, like a tire. It will need replacing over its life, and that’s on the homeowner, not a defect. We’d rather tell you that up front than have you find out later.
Frequently Asked Questions
Are battery-backup sump pumps required by law in New Hampshire?
No. New Hampshire follows the 2021 building code (IBC/IRC), and no NH law or building code requires a battery-backup sump pump. We recommend one anyway, because of how often NH storms knock out power right when your basement is taking on water.
How long does a battery backup run during a power outage?
It depends on the battery and how hard the pump has to cycle — a steady drizzle runs it far longer than a downpour. In our experience, a fully charged backup battery will move roughly a full swimming pool’s worth of water before it runs down: on the order of 15,000 to 20,000 gallons, the volume of an average residential in-ground pool. That’s a lot of storm to outlast before you’re exposed.
Battery backup vs. water-powered backup — which is better for a NH home?
Battery suits most New Hampshire homes. A water-powered backup needs strong municipal water pressure, which a lot of Seacoast and well-served homes don’t have. Battery works in any home, which is why it’s our default.
What happens to my basement if the sump pump loses power during a storm?
The pit fills, and water comes into the basement. FEMA calculates that one inch of water can cause about $25,000 of damage, and the EPA notes mold can start within 24 to 48 hours on a wet surface. A backup pump is what stops that during an outage.
How do I know if my primary sump pump is failing?
Look for a stuck float, a missing or backwards check valve, a frozen or clogged discharge line, or a pump that runs constantly. Don’t bother with the “pour test” — for a pump that keeps running, it tells you nothing.
Is the battery covered under 603’s warranty?
The sump pump system carries a 3-year warranty, but the battery is excluded. A battery is a wear item and will need replacing over time, like a tire.
Get your system checked
If you’ve got a sump pump and no backup, that’s worth a look before the next storm. We do free inspections and free estimates, and you’ll have a written quote within 24 hours. No pressure, and we’ll tell you straight whether you need a backup or not.
