The Questions Illinois Homeowners Ask Before Saying Yes to Whole-Home Battery Backup

The electricity grid in Illinois is experiencing its most punishing year in more than two decades. By ComEd's own count, the storms that rolled through on August 9–11 were the nineteenth major weather event to hit its customers in 2026—the most in more than two decades—and Illinois has recorded more tornadoes this year than any other state. A single June system knocked out power to more than 674,600 customers and took nearly 500 replacement poles to repair.  

At the same time, the supply side of a ComEd bill went in the wrong direction, too—ComEd's residential Price to Compare rose to 10.399 cents per kWh on June 1, an increase of roughly 9%. The rate will reset again on October 1, 2026.  

With all of this in mind, it isn’t a surprise that home battery backup has gone from a curiosity to a topic that your neighbor has an opinion on. What is surprising is how little of the available information answers the questions people actually ask.

These are those five questions, answered in the way we’d want them answered if it were our own house. Below each answer, we’ve also added how Energywell specifically applies it our Illinois battery program.

1. How does a whole-home battery backup system actually work?

A whole-home battery backup system, sometimes called a home energy storage system, stores electricity in one or more battery cabinets and begins powering a customer’s home with stored energy the moment the grid fails.

Most battery backup systems connect to your home between your ComEd electric meter and your electric panel. When grid power is disturbed or disconnected, your home automatically switches from drawing power from the grid to drawing power from the battery. During short grid disturbances, like the ones that might cause your lights to flicker, and during short outages like what sometimes happens during local thunderstorms, you likely will not even notice the battery taking over. No manual activation of the backup power is required—it just works.

When the battery is not being used for backup power for your home, some providers might use the battery system to provide grid services, like charging the battery when the grid has excess supply and providing power to the grid from the battery when grid supplies are tight. This is better known to some as a Virtual Power Plant, or VPP.

For most home battery systems, three major components do the bulk of the work. The batteries hold energy, measured in kilowatt-hours (kWh). The inverter converts that stored DC energy into the AC your house runs on, and its rating in kilowatts (kW) sets the ceiling on how much you can draw at once. The smart panel decides which circuits get served, and in what order, when energy supply is finite.

How Energywell does it:

Our system works as described above. Our system switches your home over to your backup automatically, and you go from drawing power from the grid to using the stored energy in your batteries—we mean it when we say you probably won’t even notice that you would have otherwise lost power. There’s nothing for you to do and nothing for you to manage.  

When the battery system isn’t powering your home, Energywell uses it to support the grid, charging when grid demand is low, and drawing on it when demand is high. Energywell adjusts your bill each month so that you only ever pay for the electricity that you actually use.

2. How long will a home battery power your house during an outage?

Simply put, runtime is division: stored energy divided by draw. This simple formula governs how long your battery lasts in an outage: (battery kWh × state of charge) ÷ household draw in kW = hours.

State of charge is how full the battery happens to be at that moment, and on a managed program that is not always 100%. When the battery isn't backing up your house, the provider is using it, typically charging overnight when grid demand is low and drawing on it in the early evening when demand peaks. So, its charge level when an outage starts depends on what it was doing an hour earlier. Household draw depends on what is running: a refrigerator, a router, and a few lights are a different load than central air and an electric dryer.

A 20 kWh system at full charge running essentials—a refrigerator, internet, lights, phone charging and a furnace fan—should be enough to power a detached home through most short-term outages. Stretching home backup power is mostly a question of what you choose not to run, so the most effective move is to reduce high-draw appliances like HVAC, EV charging, electric dryers and dishwashers. A smart panel can help prioritize which circuits stay served as stored energy depletes.  

If it is helpful, ComEd's own restoration numbers help to reinforce the case for battery backup. Localized outages are routinely restored the same day, but multi-county storm events are a different beast. After the August 11 storms, ComEd's published estimate was 80% of affected customers restored by midday August 13 and roughly 99% by the night of August 15—a four-day window from first outage to substantially complete. The June event followed a similar arc. So, while a battery will help you weather some outages, it doesn’t mean you shouldn’t plan for, well... weather.

How Energywell does it:

The standard Energywell system configuration for a medium sized home is 40 kWh, which is enough power to cover the length of most short-term grid outages. For longer grid outages, adjustments like setting your air conditioning setpoint a few degrees higher, avoiding high usage appliances like clothes dryers and electric ranges, and pausing things like EV chargers and pool pumps can extend your coverage.

3. What size whole-house battery backup do you need?

Residential battery systems are typically sized for the home based on usage required, size of home, space available for a battery system, age of electrical wiring, and other factors. Bigger is usually better and batteries typically are sized individually, commonly a single battery could be 10 kWh of storage and scale up from there. And of course, a bigger battery system also needs an inverter sized to meet demand.  

How Energywell does it:

Energywell installs 40 kWh systems, if space allows for it; smaller homes, or homes with less available installation space, may opt for a 20 kWh system. Every configuration comes with a 24 kW inverter. Energywell works with the homeowner up front to make sure the system is a good fit for the home and its typical electricity usage.

4. How much does a home battery cost, and how do no-upfront-cost programs work?

The cost of a whole-home backup system is more than the cost of a battery. It’s the battery, an inverter, a smart panel, and any required electrical upgrades and the cost of labor to install and configure the system. Bought outright, professionally installed battery backup systems for home use in the 20–40 kWh range can run between $15,000 to $30,000 for hardware and installation and can cost much more depending on the size and manufacturer. The no-upfront-cost programs now operating in Illinois eliminate that number by changing what you're buying: the provider retains ownership of the equipment and you commit to a long-term energy supply and battery services agreement instead.

There are primarily two different models for getting a backup battery for home use.

Homeowner owned battery system. You own an asset, you control and manage it, you carry the maintenance and replacement risk, and you've made a five-figure decision.  

VPP program or third-party ownership. These programs offer Illinois homeowners the benefits of backup generation for their homes without the hassle of equipment installation and maintenance because the provider owns the battery throughout the life of the contract and handles the maintenance and warranty. In exchange, you typically sign a long-term energy agreement.

It's worth understanding how a provider can afford that, because it isn't generosity. In a VPP model, the battery is an active participant in the energy grid, not just a storage device waiting for a storm.  

Charging when the grid has excess supply, discharging when supplies are tight. That coordinated use reduces how much electricity has to be bought during high-price periods and lowers exposure to costs tied to system peaks, which means a home with a managed battery costs less to serve than a comparable home without one. That difference is what pays for the hardware, and it's the reason the offer exists at all.

How Energywell makes this work:

Two things help make Energywell's no-upfront-cost offer work. First, the State of Illinois has put financial incentives in place for the installation of home battery systems, in part to help combat rising electricity costs for residents, and those incentives help Energywell cover part of the installation cost. Second, Energywell operates its batteries as part of a networked fleet. The grid services the battery provides help Energywell lower the cost to serve its electricity supply customers, which is what allows those savings to be passed along to you.

5. Will a home battery lower my ComEd bill?

No. A battery by itself won’t reduce your bill, particularly in an ownership model—but what can impact your monthly bill is your electricity supply plan.  

How Energywell does it:

As an Energywell electricity supply customer, your electricity supply rate will always be lower than ComEd Price to Compare. After your battery system installation is complete and your account is switched to Energywell, you will receive a discount versus ComEd's Price to Compare of 25% during on-peak hours (5am–10:59pm CT) and 28% during off-peak hours (all other hours).  

ComEd continues to manage delivery and send your monthly bill, but the supply line will change to Energywell's discounted rate. Energywell also credits you for the electricity direct consumed by your battery system, so your total bill reflects your home’s electricity consumption each month.

Your total bill amount can change seasonally based on the amount of electricity your home uses, but you will always pay less with Energywell for electricity supply than you would have if you were on ComEd’s Price to Compare.

‍

Key takeaways

• Whole-home battery backup—also called home energy storage—takes over the instant the grid drops, no generator or manual switch required. For most short outages, you won’t even notice it happened.  

• How long a battery lasts in an outage comes down to simple math: capacity x state of charge ÷ household draw. That’s why “guaranteed runtime” from any provider is worth a hard look.  

• Behind most no-upfront-cost battery programs is a Virtual Power Plant (VPP); the battery earns its keep between outages by charging when the grid has excess supply and discharging when demand peaks, and that value is what funds the hardware.  

• Whole-home battery backup ownership cost runs roughly $15,000–$30,000 installed for a fully-equipped 20–40 kWh system. No-upfront-cost programs replace that price with a long-term energy agreement, letting the provider run it as part of a coordinated fleet. A battery itself doesn't lower your bill, but Energywell’s supply rate ensures that you’re not paying more than ComEd’s Price to Compare.

• Energywell's standard configuration, up to four battery modules, is built to cover short outages for most residential homes.

• ComEd keeps managing delivery and billing either way—becoming an Energywell customer only changes the supply line on your bill.

‍

‍

_{DISCLOSURE: Backup power duration depends on the battery's charge level at the start of an outage, and the rate of energy consumption during the outage. Higher charge levels and lower usage will result in longer backup duration. Constant backup power not guaranteed for the full duration of every outage. Retail electricity products offered by Fanfare Energy, LLC d/b/a Energywell (Illinois Commerce Commission Docket No. 26-0381). Battery management services offered by Energywell Home, LLC (“EWH”). Fanfare is an independent Alternative Retail Electric Supplier (“ARES”) and is not affiliated with, endorsed by, or acting on behalf of ComEd, any consumer group, or any governmental body or program. You are not required to enroll with Fanfare. Beginning on June 1, 2026, the electric supply price to compare is 10.399 cents per kilowatt-hour. The electric utility electric supply price will expire on September 30, 2026. The utility electric supply price to compare does not include the purchased electricity adjustment factor. For more information go to the Illinois Commerce Commission's free website www.pluginillinois.org. The purchased electricity adjustment factor may range between +.5 cents and -.5 cents per kilowatt hour. Fanfare and EWH offers are not available in all U.S. jurisdictions and may vary or be discontinued at any time.}

‍