Do home batteries pay for themselves yet? Running the arithmetic

The core identity

Extra self-consumed kWh ≈ min(usable capacity × round-trip efficiency × cycles/year, kWh you currently export)

Annual saving ≈ extra self-consumed × (grid price − export price)

Payback ≈ battery cost ÷ annual saving

The life check

If payback exceeds cycle_life ÷ cycles_per_year, the pack may hit its cycle limit before it has paid for itself — on those assumptions.

What this model ignores

Peak shaving for demand charges, backup value, tariff arbitrage without solar, and degradation of capacity over time. Those can matter. Add them manually if they apply to you.

Open the battery ROI calculator and stress-test the spread and exported kWh first.