Sump pump in a power outage: 4 ways to keep an Illinois basement dry

Short answer: a sump pump is useless in an outage unless something else powers it. You have four options: a battery backup pump (the cheapest), a water-powered backup pump, a portable generator with a safe hookup, or a home battery that also runs your fridge and furnace. If all you worry about is the basement, the cheap option is often enough, and we'll say so.

Why storms and outages arrive together

The heavy rain that fills your sump pit and the wind that takes down power lines usually come in the same storm. In the August 11–12, 2026 storms alone, ComEd reported about 410,000 outages (ComEd, Aug 15, 2026). For a house with a basement, that's the worst timing possible: the pump stops exactly when the water comes.

How much power does a sump pump need?

It depends on the pump size and how often it cycles. In a heavy storm it can switch on every few minutes; on a dry day it may not run at all. Our backup calculator plans for about 2.5 kWh per day for a sump pump during a storm. That's a planning number, not a measurement of your pump. To get closer for your home:

• look at the label on the pump (1/3 hp and 1/2 hp are common);
• in the next heavy rain, count how many times it starts in 10 minutes.

The four options

Option	What it keeps running	Typical cost	Good to know
Battery backup sump pump	A second pump in the pit, on its own 12-volt battery	about $600–2,000 installed	Only the pump. The battery needs checking and replacing every few years.
Water-powered backup pump	A backup pump driven by your city water pressure	ask a plumber	No battery, but it needs municipal water with enough pressure and uses water while it runs. Check local plumbing code.
Portable generator + safe hookup	The pump plus a few circuits, through an inlet and interlock installed by an electrician	generator + electrician	Never in the garage or near the house: the CDC says more than 20 feet away from your home, doors and windows (CDC). Someone has to be home to start and refuel it.
Home battery (about 13.5 kWh)	The pump plus the fridge, lights, Wi-Fi and the furnace fan, automatically	about $11,500–16,500 before incentives	Switches over by itself, silently, even when you're away. Biggest cost.

Costs are typical ranges we've seen in Illinois, not quotes. Your home can be cheaper or more expensive.

How long would a home battery keep the pump going?

A typical home battery holds about 13.5 kWh, and roughly 90% of that is usable (about 12 kWh). Using the same planning numbers as our calculator:

• sump pump only (2.5 kWh/day): about 4–5 days;
• pump + fridge + lights and Wi-Fi (5.5 kWh/day): about 2 days;
• all of that + the gas furnace fan in winter (9.5 kWh/day): about 1¼ days.

Solar panels on the roof stretch that, even on cloudy days, but on their own they shut off in an outage (a safety rule for line workers), so the battery is what keeps the pump running. You can try your own mix in the calculator.

Which one fits you?

1. Only the basement matters, and outages are short: a battery backup sump pump. Cheapest per dollar of protection.
2. City water, and you want no batteries at all: ask a plumber whether a water-powered backup works with your pressure and code.
3. You're home during storms and fine with refueling: a generator with a proper inlet/interlock. Never a cord through a window.
4. You want everything essential to just keep working, also when you're away: a home battery, often combined with solar.

Before the next storm (free checklist)

• Test the pump: pour a bucket of water into the pit and watch it start and stop.
• Check the discharge line outside: not frozen, not blocked, draining away from the house.
• Look at the check valve (it stops water flowing back into the pit).
• Install a CO detector near every sleeping area if anyone in the house will ever run a generator; the CDC recommends battery-operated or battery-backup detectors.
• Ask your insurance agent whether water damage from a failed sump pump is covered. On many policies it's a separate add-on, so check yours.

How we're paid

Lights On Illinois is paid by licensed installer partners when someone buys an installation through us. That's exactly why we tell you when the $600 option is enough: we'd rather you trust us for the next decision.

Sources

• ComEd press release on the August 2026 storms (Aug 15, 2026): stockwatch.com
• CDC, "When the power goes out, keep your generator outside": cdc.gov
• Planning numbers (kWh per day, 90% usable battery capacity): the Lights On Illinois backup calculator assumptions
• Price ranges: our 2026 research on Illinois installation prices (typical ranges, not quotes)