Ask these 7 questions before you buy a home battery

Canary Media’s Electrified Life column shares real-world tales, tips, and insights to demystify what individuals can do to shift their homes and lives to clean electric power. 

This article is the second in a two-part series on home batteries. In case you missed it, here’s part 1: ​“Is adding a battery to your rooftop solar worth it? Here’s how to decide.”

Alex Bazhinov has turned his home into a clean energy power plant, complete with the ability to store renewable energy for when he needs it. The solar panels on his roof in Charlottesville, Virginia, feed his home battery during the day, so it can charge his electric vehicle in the evening. This allows him to avoid the cost of charging from the grid; plus, he said, ​“I know that I’m driving on truly clean electricity.”

Besides their ability to deliver renewable power, home batteries can provide resilience in the face of outages and deliver a quicker system payback than installing rooftop solar alone. And while home batteries are still expensive, for the first time, their costs are coming down, Charles Hadlow, president and chief operating officer at clean energy marketplace EnergySage, told Canary Media. 

Based on over 300,000 EnergySage battery system installation quotes done through the platform, costs tumbled from the first half of 2023 to the second half from a median of $1,352 per kilowatt-hour (kWh) stored to a median of $1,265.

Thanks to these falling costs, a changing policy landscape, and a bevy of incentives, batteries are becoming a hot home addition. In 2020, the number of solar customers also installing home batteries hovered below 10% nationwide. Now that rate has shot to more than 30% — in large part because Californians are flocking to batteries amid a new regulatory regime that incentivizes them. Texas and Florida are also moving the market, potentially driven by extreme weather, Hadlow said.

If you already have rooftop solar — or are planning to get it — and you’re intrigued by a home battery’s benefits, you’ll have a number of factors to consider first. Buying a battery is like buying a car — only, how to evaluate batteries is less familiar.

So here are seven key questions to ask yourself before you get a home battery of your own.

1. How much stored energy, or capacity, do I need?

Batteries have two major features: their capacity (how much energy they can store) and their power rating (how fast they can deliver that stored energy). Think of the battery’s capacity like a tank of water; the power rating is like the size of the pipe that drains it.

An average home uses 29 kWh per day, and a typical battery stores 10 to 13 kWh. To determine how many batteries will cover your needs, a good contractor will use software to analyze your energy consumption data from your utility, said Barry Cinnamon, CEO of California-based Cinnamon Energy Systems. The system size will also be influenced by how you answer this next question.

2. What appliances do I want to back up? 

Different appliances have distinct power requirements. A Wi-Fi router takes less power to run than a refrigerator, which takes less power than an air conditioner or a sump pump. Appliances also have different needs for peak or surge power (like when an AC kicks on) and for continuous power (to keep the AC running over time). If the devices you plan to back up are power hungry, you’ll want to make sure your battery is rated to provide for their peak and continuous power needs.

These power ratings ​“are changing pretty fast,” Hadlow said. ​“Some of the latest batteries coming out, such as the PowerWall 3, Franklin Whole Home [aPower], and Enphase IQ 5P, are significant improvements over what we’ve seen in the past.”

Some models can be stacked to increase their power output, while for others, that’ll only increase their capacity. The Enphase IQ batteries, for example, scale: while one delivers 3.84 kW, two together will output 7.68 kW. 

3. How much flexibility do I want?

If you plan to use a battery during power outages, then keep in mind that you’ll generally need to choose which four to seven appliances or ​“loads” might be critical to keep on. If you’re ready to decide now and don’t plan to change them, then your contractor will hard-wire them into a critical-loads panel. 

“Only the loads that are on that panel can be backed up by your battery,” said Emily Walker, the senior writer at EnergySage who leads its consumer education strategy. 

But there’s an alternative: smart panels. These devices ​“can help you dynamically shift your load so that you don’t have to decide from the start exactly what you want to back up,” Walker said. Options include products from startups Span, Lumin, and Koben and multinational corporation ABB in partnership with Lumin.

A home energy management system also allows you to more easily participate in programs that pay customers to send power to the grid, explained Bazhinov, founder and president of Lumin. When the grid is stressed, a smart panel can pause flexible loads for a couple of hours, like charging your EV or running your dishwasher, thereby minimizing what you consume yourself and maximizing energy exports. That allows you to get paid more.

Smart panels aren’t cheap, however. They can cost $2,500 to $3,500 for the equipment alone, with installation adding on another $1,000 to $1,500, depending on the complexity of the work and the local labor market, according to Spencer Fields, director of insights at EnergySage.

4. What other battery system hardware might I need?

Another factor to keep in mind is that if you want to use your battery during a blackout, it’ll need to be able to disconnect from the grid. If your home can’t ​“island” itself, your solar panels and battery will push power back into those lines — with potentially fatal consequences: Lineworkers who assume that the lines are dead can get electrocuted.

To sever the grid connection, you’ll need a transfer switch. ​“If there’s no power coming from the utility,” Cinnamon explained, ​“you hear this ka-chunk” as it physically disconnects. The price of that independence can come at around $3,000 to $4,000, he noted.

5. What type of battery should I get?

Though lead-acid batteries will work, the most popular batteries to pair with solar have lithium-ion chemistries that make them more energy dense and longer-lived. Two lithium-based chemistries dominate: lithium nickel manganese cobalt oxide, called NMC, and lithium iron (Fe) phosphate, called LFP. 

NMC is today’s most common battery chemistry, but LFP is gaining popularity, Hadlow said. LFP batteries are less energy dense and tend to cost more per kWh, but they are more stable, and thus safer; are longer lasting (up to 20 years of daily use); and don’t put out as much heat, so they can be installed indoors with basically no risk, Walker said. Another battery chemistry to put on your radar: lithium titanate (LTO), she added. With a higher price point, LTO batteries are reputed to be even safer and longer-lived than LFP batteries.

6. Does the battery system I’m interested in have a good warranty? 

Battery warranties usually cover the equipment (though not installation) cost of replacing a battery if it malfunctions within a certain number of years, a total energy throughput, or a number of cycles — the number of times a battery recharges after dipping below a certain threshold — whichever comes first. Manufacturers usually warranty a lithium-ion battery for at least 10 to 12 years. As a battery ages, its capacity also degrades. Manufacturers may specify how much energy you can expect the battery to still be able to store at the warranty’s end. Look for at least 60%, according to Fields.

7. Where am I putting a battery system?

You’ll want to make sure the battery you get is suited to where you install it. Some battery enclosures aren’t rated to withstand the elements and need to be placed indoors. Just make sure the installation complies with building and fire codes, Fields said. And for outdoor batteries, you don’t want to put them in direct sun, which could make them overheat.

The local environment may also influence what battery you choose and where you plonk it: If you live near the beach, salt water can corrode a battery’s casings, voiding the warranty. Other batteries can’t handle the high altitudes of the Rocky Mountains. For a well-reviewed installer, this won’t be their first rodeo; you can lean on them to recommend batteries well suited to your locale.

Taking the next step

If and when you’re ready to shop around for a home battery, remember to get at least three quotes, Walker said. The EnergySage marketplace provides them for free.

While home batteries carry big price tags, they might be worth it for you. If you have solar, they let you soak up every watt of clean power you generate — and that can pay dividends in lower energy bills, enhanced resilience, and a cooler climate.