Choose your state
Ranked by payback on a 13.5 kWh battery, assuming you also have solar.
Double-counting the battery. A battery cycles about once a day. It can shift cheap off-peak power into peak hours, or hold your solar until evening — but the same stored kilowatt-hour cannot do both. Quotes that list both savings and add them together are selling you one battery and charging for two.
Free electricity. Round trips lose about 10%, so delivering one kilowatt-hour means buying about 1.11. Left out, that overstates arbitrage by roughly 11% before anything else.
There are 5 states where a battery has no bill-saving mechanism at all — full retail net metering means the grid already stores your solar for free, and with no time-of-use tariff there is no spread to trade. Those pages say so plainly.
None of this is an argument against buying one. Outages are real, storage incentives can be worth thousands, and keeping the lights on has a value no spreadsheet sets. Just buy it for the right reason.
Data vintage: Electricity: EIA Electric Power Monthly Table 5.6.B (residential, May 2026 YTD). Solar resource: PVGIS v5.3 (EU JRC), ERA5 2005-2023. Gasoline: AAA state averages. Natural gas: EIA residential by state. Heating degree days: NOAA CPC population-weighted normals. Retrieved 2026-08-03/04. Install costs, household usage, net-metering status, annual mileage, time-of-use spreads and outage hours remain estimates.