1. List critical loads and hours (fridge, sump, router, LEDs). Convert to daily kWh (watts × hours ÷ 1000).
2. Pick backup hours/days. Required **usable** capacity = daily kWh × backup days (e.g., 2.1 kWh/day × 2 = 4.2 kWh).
3. Adjust for DoD and efficiency. Nameplate ≈ usable ÷ (DoD × efficiency). LiFePO₄ at 90% DoD and 92% efficiency: 4.2 ÷ 0.828 ≈ 5.1 kWh.
4. Inverter power. Size continuous output for your biggest running load plus surge (2–3× for pumps).
5. Cost bands. Batteries ~$350–$600/kWh; hybrid inverter $900–$2,500; balance‑of‑system $500–$2,000. Labor varies by region.
6. Payback thinking. If you arbitrage TOU rates or pair with solar, savings offset some cost. Use a simple spreadsheet to model.
**Pro tips**
• Consider DC‑coupled vs AC‑coupled when integrating with existing solar.
• Check warranty cycle life and ambient temperature limits.
**CTA**
Download our free sizing sheet for home battery backup lifespan calculator and compare real‑world kit prices.
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