Buyer's guide

Home batteries: continuous power, not usable kWh, is the spec buyers get wrong

A battery can hold plenty of energy and still fail the one moment you bought it for -- because the spec that predicts whether it can start your well pump or your AC isn't the kWh number on the box.

kWh tells you how long. Continuous kW tells you whether it works at all.

Usable capacity (kWh) is the number every listing leads with, and it answers a real question -- how long can this run my house. But it isn't the number that decides whether the battery can carry your house in the first place. That's continuous power output (kW), and separately, whether the battery and its inverter can handle a motor's starting surge, not just its steady running draw.

A real, documented case makes this concrete: a correctly sized and professionally installed system -- an LG Chem battery paired with a SolarEdge inverter -- could carry a well pump's steady-state running current without trouble, but could not start it. A motor's starting current can run six to eight times higher than its running current for a fraction of a second, and if the inverter can't cover that surge, the pump simply won't start on battery power, no matter how much energy is sitting in the battery. No kWh figure, and no continuous-kW figure alone, warns you about this -- it's a property of the specific inverter and the specific motor together, and it's worth asking your installer directly whether they've sized for starting current, not just running load.

The mirror-image mistake is just as common, and just as easy to make from a spec sheet alone: some buyers add up the breaker rating of every circuit they want backed up -- in one real, documented case, 135A across a panel, or about 16.2kW -- and compare that against a single unit's rated continuous output, like a Powerwall 2's 5kW. That comparison overstates the real risk by more than 3x, because you're extremely unlikely to run every backed-up circuit at its full breaker rating simultaneously. The right calculation is realistic simultaneous load, not summed breaker capacity -- and it's a conversation to have with your installer before you assume you're undersized, not just before you assume you're covered.

You're also betting on the company, not just the hardware

A home battery is typically a 10-15 year commitment, installed once and expected to keep working with minimal attention. That makes manufacturer viability a real buying consideration, not a paranoid one. SunPower filed Chapter 11 in 2024, leaving real, named homeowners with a non-functional battery and monitoring system in their basement and no clear support path. Panasonic exited the US residential solar and storage market entirely in 2025 -- a company most buyers would have assumed was too large to simply leave the category. A broader review published in mid-2026 named nine real solar/storage companies that failed within the prior two years, a wave tied in part to the same federal tax-credit termination covered below, which compressed margins across the industry at once.

None of this means avoid smaller or newer manufacturers -- some of this catalog's best-specified products come from companies with shorter track records. It means ask directly: how long has this manufacturer been selling battery storage in the US, what happens to my warranty if the company is acquired or exits the category, and is the installer independent of the manufacturer or a captive/exclusive dealer who might not be there either if the manufacturer leaves.

Two real recalls, and a safety remedy that can itself leave you without power

Battery fire and overheating risk is not hypothetical, and it's worth knowing the two real, current examples on file rather than a vague sense that "batteries can catch fire." The CPSC recalled roughly 10,500 Tesla Powerwall 2 units in November 2025 for a fire and burn hazard -- units that could overheat and, in some cases, smoke or catch flame during normal use. LG Energy Solution recalled its RESU 10H battery in 2022, about 11,500 units, for the same class of risk.

What makes the Tesla case worth understanding in more detail is the remedy itself. A filed class action (Brown v. Tesla, Middle District of Florida, November 2025) alleges that Tesla's actual fix for affected units was to remotely discharge them to near-zero charge to reduce fire risk -- which is a genuinely reasonable safety response, but one that also leaves the owner without any working backup power, in some cases for months, while a replacement is arranged. The safety fix and the reason you bought the product can be in direct tension. A second filed complaint (Haak v. Generac) alleges a near-50% failure rate on a rapid-shutdown component in an unrelated product line, a different failure mode but the same underlying point: read the recall and complaint history for a specific manufacturer and chemistry, not just the brand's marketing.

The two recalls above both affected nickel manganese cobalt (NMC) chemistry products. Lithium iron phosphate (LFP) is the chemistry most manufacturers have since standardized on for home storage specifically because it carries a wider thermal-safety margin -- if fire safety is a priority for you, ask directly which chemistry family a specific product uses, rather than assuming.

There is no ENERGY STAR or AHRI-equivalent certification for this category

Unlike furnaces, heat pumps, or central air conditioners, no independent certification or test program verifies a home battery's claimed specifications -- including round-trip efficiency, the one figure this pass found genuinely disputed across sources for more than one product. This is worth stating plainly because it's easy to assume otherwise: energystar.gov hosts a federal tax-credit information page that uses "ENERGY STAR" language in connection with battery storage, but that page describes a tax credit, not a certified-equipment testing program the way ENERGY STAR functions for other appliances. There's no independent directory to cross-check a manufacturer's claimed efficiency or capacity figures against, the way AHRI's public database works for HVAC equipment. Treat every spec on a battery's page as the manufacturer's own claim until you find independent corroboration.

Outdoor siting can throttle real-world output when you need it most

A battery sited outdoors, even in a fully code-compliant, installer-recommended location, can thermally derate under real heat -- a documented Arizona case showed output throttling to roughly a third of rated continuous power during peak summer afternoons. That's exactly the moment a household's air conditioning load, and therefore the entire reason many buyers wanted backup power in the first place, is highest. This isn't a defect in any specific product; it's a siting and climate question. If you live somewhere that gets seriously hot and you're depending on the battery for AC backup, ask your installer directly what siting they're proposing and whether it accounts for real summer afternoon heat, not just the equipment's nameplate rating.

The federal tax credit for a new system ended December 31, 2025

The 30% uncapped federal tax credit (Section 25D) that made battery storage economics work for many households terminated for any system placed in service after 2025-12-31, under the One Big Beautiful Bill Act. If an installer's quote leans on that credit to justify the price, confirm directly whether your specific installation will actually be placed in service in time to qualify -- and get any completion-date promise in writing as a contract term with a real remedy attached if it slips, not a verbal assurance. Installer scheduling delays that miss a hard regulatory deadline are a real, recurring complaint, and once the deadline passes there's no retroactive fix.

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