Methodology

Usable energy has no single basis

A battery’s usable energy is published by its manufacturer, by government lists, and by test labs, and they do not measure it the same way. A government list may give cell arithmetic. A spec sheet may state energy at beginning of life. A test lab measures what one sample delivered. So this site never picks one as the true number. It shows each one with its source.

Who says it

Every figure belongs to one layer, named beside it.

• Manufacturer: the product’s own spec sheet or warranty, cited with its page.
• Listed: a government or program list, such as the Japanese SII list.
• Measured: an independent lab or field test.

The collected figures total 1,176 for 92 products. Of these, 1,173 are from manufacturers, 3 are from government and program lists, and none are yet from independent measurements.

How the figures are sourced

Values and ranges in the comparison table

Each cell of the comparison table shows what one layer publishes, chosen by a fixed order of layers: the manufacturer first, then the California, Australian and Japanese lists, then measurements. Where that layer publishes several values, such as the sizes of one product family or the output settings of one unit, the cell shows the range from the lowest to the highest rather than picking one end. The warranty years, warranted throughput and capacity at warranty end in one row come from one document, so a row never combines terms from two editions. The table never averages. When other documents or layers publish a different value, the cell says how many, and the product page shows every one.

Rules for the numbers

• Source percentages retain their stated precision. Derived usable shares are truncated to whole percent.
• A median installed price is shown only when at least 20 priced installs stand behind it.

Review status

The lists supply 3 figures directly. They need no transcription check.

Of 1,173 transcribed figures, 109 have been checked against their document. The remaining 1,064 are marked “Not yet checked”.

A transcribed figure without a captured quote says “page cited, no quote”.

Feature comparisons

Energy, power, efficiency, and temperature charts pair manufacturer figures from the same document, configuration, and capacity basis. Claims are paired only when their markets match or one market is unspecified. A range without a configuration pair has no dot. Energy, power, efficiency, and temperature charts require at least 20 batteries with matching figures. Temperature charts use each document’s stated low and high limits.

The counts below separate batteries with matching figures from those without a matching configuration.

• Nominal energy and continuous power: 30 batteries with matching figures. One more has figures without a matching configuration. Offered as a chart.
• Nominal energy and peak power: 15 batteries with matching figures. One more has figures without a matching configuration. Not offered as a chart.
• Nominal energy and round-trip efficiency: 21 batteries with matching figures. None have figures without a matching configuration. Offered as a chart.
• Charging temperature: 33 batteries with matching figures. None have figures without a matching configuration. Offered as a chart.
• Discharging temperature: 31 batteries with matching figures. None have figures without a matching configuration. Offered as a chart.
• Operating temperature: 50 batteries with matching figures. None have figures without a matching configuration. Offered as a chart.
• Usable energy and continuous power: 22 batteries with matching figures. None have figures without a matching configuration. Offered as a chart.
• Usable energy and peak power: 13 batteries with matching figures. None have figures without a matching configuration. Not offered as a chart.

A manufacturer’s quote is shown only after a reviewer confirms or corrects the claim against its document. Unchecked figures retain the value, document link, page, and retrieval date. The pages show 185 quotes. Quotes include claims that are not figures, such as listings and warranty terms. The remaining 1,568 quotes wait until a reviewer has checked them.

Warranty terms come from one chosen document. The document stating the most warranty terms is chosen. If the counts tie, ties go to a warranty document, then the newest dated document. A remaining tie is broken by document name. A conditional throughput is stated with its condition and has no dot. Total MWh is the stated MWh. Where the warranty states MWh per usable kWh, that figure is multiplied by the usable energy of the same configuration. Throughput per stored kWh or per net-capacity kWh is not normalized unless the document names that capacity. Full-cycle calculations may pair a warranty with a capacity figure from another document for the same model and market. Full cycles are total MWh multiplied by 1,000 and divided by usable kWh, or nominal kWh when no usable figure is stated. Only US, global, and unspecified-market terms enter the warranty chart.

A stack maximum is the maker’s stated maximum. Unit energy is never multiplied by the unit count. Usable share pairs single values from the same document and configuration. Usable shares are truncated to whole percent. Equal figures carry no share. Usable energy above nominal energy carries no share.

Recalls

Notices from the US Consumer Product Safety Commission, Australia’s ACCC and the UK Office for Product Safety and Standards are quoted with the authority’s title and remedy. A marker appears on the product matched to each notice. The site holds 11 notices. An unmatched notice stays on the recall hub. A product with no matched notice has not been found safe. Listing and test claims are the maker’s statements and have not been checked against a listing body’s records.

Connecticut prices cover residential installations matched to a product and naming a battery model. The program’s flags for pre-existing storage and transfer from Connected Solutions determine which projects count. Either positive flag identifies an existing battery. Both negative flags identify a new installation. One negative flag with the other blank leaves the installation unclassified. Dates and installation stages decide only when both flags are blank. Years follow the approval year. An install without an approval year appears only in the all-years total. Its count is stated beside that total. Pairing separates solar-paired and standalone installations. An unspecified pairing contributes to the total only. Every measure needs at least 20 positive prices before its median or middle range is shown. The middle range is the 25th to 75th percentile, using continuous quantiles. Battery cost per kWh divides battery cost by the program’s reported battery energy. The program does not label that energy as nominal or usable. Contract price may include other equipment. Up-front incentives are stated separately. No project, town, or ZIP appears in the published aggregates.

Search matches the curated battery names, configurations, alias prefixes, and part numbers. Generic category words and brand-only names do not become model keys.

A battery pair has a comparison when people search for the two batteries together at least 100 times a month.

Starting current stated as locked-rotor amps or RMS is compared with the reader’s nameplate locked-rotor amps. Peak amps and currents with no stated basis are shown separately. Equal or greater current goes in the “at least” group. Each configuration keeps its stated figure. No current is multiplied by a unit count. Surge power and peak power remain separate quantities.

Climate

Climate counts use 2015–2024 station observations. A usable year has at least 350 days with both daily extremes, and a station needs at least 8 usable years. The station matches cover 30,949 US ZIP areas using 1,705 stations after this rule. Each count averages the days strictly below or above a stated limit over usable years and truncates to whole days. The temperature filter checks for any observed day outside the limits before truncation. A displayed zero can therefore include rare days outside a limit.

The ZIP match uses the climate source’s station assignment. Heating design temperature is the temperature exceeded during 99% of hours. Cooling design temperature is exceeded during 1% of hours. Counts describe station outdoor air, without a garage or indoor-temperature model and without an output-reduction model.

Climate attribution

• NOAA NCEI Integrated Surface Database (ISD-Lite). Derived from NOAA observations by this project. Not NOAA data, and not endorsed by NOAA.
• Hourly surface weather observations from the named stations, 2015 to 2024
• U.S. Census Bureau geography. The Census Bureau supplied the original geography. This project calculated the estimates.
• USGS 3D Elevation Program

Backup hours

Backup hours divide stated usable energy by the selected load, starting full. Above continuous power, no runtime is calculated. Appliance figures are the 2012 DOE Energy Saver nameplate maximums, not average household demand. Only sourced rows are offered. All other loads require watts entered by the reader. Solar recharge, reserve settings, and inverter and battery losses are outside the arithmetic. The starting-power check uses the largest selected motor’s running watts multiplied by 3, plus the other loads. The DOE appliance guidance describes starting current as about three times running current during the first second. The estimate is compared with stated peak power when available. Neither this estimate nor the starting-current comparison predicts that a motor will start.

Feature attribution

• Installation counts from the Connecticut Energy Storage Solutions (ESS) Enrollment dataset, Connecticut Green Bank and PURA, via the Connecticut Open Data Portal.
• Appliance wattages from the U.S. Department of Energy, Energy Saver, "Estimating Appliance and Home Electronic Energy Use" (2012 edition, via the Internet Archive).