Today's cheapest 48V rack batteries per kWh → Solar payback →
How the math works
Each cycle the battery delivers size × usable depth kWh at the peak rate, and recharging it takes that ÷ round-trip efficiency at the off-peak rate. Saved a year = (delivered × peak − delivered ÷ efficiency × off-peak) × cycles per day × 365. Pays for itself = (size × $/kWh + other costs) ÷ saved a year. Cost per kWh stored = upfront cost ÷ (delivered per cycle × rated cycles): if it is above your peak-minus-off-peak spread, the battery will wear out before it pays back.
Choosing a state sets peak to 1.3× and off-peak to 0.6× its average rate as a rough time-of-use split; replace them with your utility's schedule. The rates, 90% efficiency and 6,000 cycles are starting values, not facts about your battery: use your utility's time-of-use schedule and the cycle rating on the battery's spec sheet. Batteries also need an inverter or hybrid inverter and, for most homes, an electrician; backup value during outages and any incentives aren't counted.
Battery price per kWh as of 2026-11-05: the middle and lowest of 40 current 48V LiFePO4 listings (Amazon, and eBay item + shipping) on our 48V battery price page.