How much does a whole home battery backup cost?

How much does a whole-home battery backup system cost installed?

Installed cost depends on battery capacity, inverter and balance-of-system equipment, installation labor, permitting, and any electrical upgrades. In its Q1 2021 benchmark, NREL estimated $15,852 installed for a 5 kW/12.5 kWh DC-coupled storage-only system and $16,715 for an AC-coupled system. Those are dated modeled costs, so treat them as a transparent reference point rather than a current local quote.

The benchmark separates the battery kit from the total installed price: the kit was approximately $6,406–$6,662. The modeled breakdown also includes inverter, electrical equipment, engineering, permitting, inspection, interconnection, and labor. That distinction matters when comparing bids: a lower battery price does not necessarily mean a lower installed project cost.

Ask for an itemized estimate with the battery pack, inverter, electrical balance-of-system equipment, labor, permits and inspections, and panel or wiring upgrades shown separately. For solar-connected systems, ask whether the quote includes the equipment and controls needed to isolate the home from the grid during an outage. The Department of Energy’s resilience analysis says islanding costs are site-specific and cites an anecdotal range of 10%–50% above a non-islandable PV-and-storage system; this is not a universal surcharge.

For a capacity reference, the National Laboratory of the Rockies’ 2025 Annual Technology Baseline uses a representative 5 kW/12.5 kWh residential battery system, based on lithium-iron-phosphate cells. Power and energy are different: 5 kW describes the system’s power benchmark, while 12.5 kWh describes stored energy. A home that needs large loads simultaneously may require more power, more storage, or both.

How long will a whole-house battery last during a power outage?

A whole-house battery lasts as long as its usable stored energy can cover the loads being served, with solar generation potentially extending runtime. The Department of Energy identifies stored energy at outage start, critical-load demand, and solar availability as key factors. There is no single runtime figure that applies to every home.

Use this quick estimate: runtime in hours ≈ usable battery capacity in kWh ÷ average load in kW. For example, a 12.5 kWh battery serving a steady 1 kW load would have a simple arithmetic estimate of 12.5 hours. This is not a promised runtime: actual usable capacity and changing appliance demand affect the result.

Start with the specific circuits you want to keep on, not the label “whole home.” Essential-circuit backup may cover refrigeration, lights, communications, and selected outlets. Partial-home backup adds more circuits. True whole-home backup aims to support the home’s broader load, but high-demand equipment can require a larger system and careful power planning.

To size energy, list each appliance’s wattage and expected operating hours, multiply those figures to get watt-hours, then add the loads together and convert to kilowatt-hours. The Department of Energy’s residential battery guide recommends this appliance-by-appliance method and also points homeowners to utility bills as a way to understand energy use. Your own bills are more useful than a national average: the EIA reports average U.S. residential electricity purchases of 10,791 kWh in 2022, while state averages varied substantially.

Can a whole-home battery backup run central air conditioning or a well pump?

It can, if the system is configured and sized for the equipment’s power demand and the energy it will use. Air conditioning and water pumps are examples of potentially critical outage services in the Department of Energy’s resilience analysis, but their inclusion can make backup sizing more demanding.

Separate two checks. First, confirm the inverter can supply the power required when the equipment operates, including any starting demand specified for that equipment. Second, estimate how many hours it will run and include that energy in the battery calculation. The provided sources do not give universal wattage figures for central air conditioners or well pumps, so use the equipment nameplate and installer’s load assessment rather than a generic appliance estimate.

Heating and cooling are among the harder loads to back up. A study by Lawrence Berkeley National Laboratory and NREL found that, when heating and cooling were included among critical loads, a modeled 10 kWh solar-plus-storage system served an average of 86% of critical load across counties and months. The study also found that modeled summer performance varied by close to 15% with central-air-conditioning efficiency, and building efficiency and household characteristics could affect backup performance by up to 20%. The result is a useful warning: the same battery capacity can perform differently in different homes.

If the system cannot support every large load, ask the installer to model which circuits can run together and which need to be managed. A practical design might prioritize a pump or cooling equipment for limited periods while preserving capacity for essential circuits. The final combination should follow the actual equipment specifications and the household’s outage priorities.

Can I add battery backup to my existing solar panels?

Often, but existing grid-tied panels do not automatically keep working when the utility grid fails. The Department of Energy explains that grid-connected solar generally shuts off during an outage for safety; producing power independently requires a properly configured inverter and storage system.

Ask the installer three direct questions: “Can this inverter operate in islanded mode?” “Is it compatible with the battery and controls proposed?” and “What transfer equipment and critical-load panel are included?” The system must detect the outage, disconnect safely from the grid, supply the selected loads, and reconnect when utility service returns. The Department of Energy describes this islanding sequence as part of a resilient solar-and-battery setup.

AC- and DC-coupled designs connect solar and storage differently. NREL’s benchmark describes AC coupling as converting solar output from DC to AC through the grid-tied inverter and then back to DC through the battery inverter. A DC-coupled arrangement uses a shared inverter. Which option fits an existing array depends on the installed equipment and the proposed battery system; request a compatibility assessment rather than assuming that panels and batteries will work together.

For outages beyond the energy already stored, solar-plus-storage can recharge from sunlight, including after stored energy is used overnight, according to the Department of Energy. Battery-only backup cannot replenish itself from sunlight. A battery-generator combination is another planning option for prolonged outages, but the sources provided do not establish a universal cost or runtime comparison for generator pairings. Compare those options against outage duration, safe system design, and the loads that must remain available.