Frequently Asked Questions
How big of a battery do I need?
Calculate critical load (refrigerator 150W, lights 200W, modem 50W, pumps as needed, furnace blower 500W) and multiply by desired backup hours. A typical "essentials only" backup for 24 hours needs 5-10 kWh; whole-home for 1 day needs 20-40 kWh. Add 20% derate for battery cycle efficiency and depth-of-discharge headroom.
What is surge vs continuous wattage?
Continuous wattage is the steady-state draw of a device (e.g., refrigerator runs at 150W). Surge wattage is the start-up spike - motors and compressors can draw 3-5x continuous for a few seconds. A 750W well pump may surge to 3,000W on startup. Your inverter must handle the surge of the largest motor; otherwise the battery shuts down on overload.
Do batteries qualify for the 30% tax credit?
Yes - battery storage with 3+ kWh capacity qualifies for the Residential Clean Energy Credit at 30% with no cap (Section 25D). The battery does NOT need to be paired with solar as of the 2022 Inflation Reduction Act update. A $14,000 Tesla Powerwall installation yields $4,200 federal credit, carried forward if not absorbed in one year.
LFP vs NMC battery chemistry - which is better for home?
LFP (lithium iron phosphate) is now the standard for home backup: longer cycle life (6,000+ cycles vs 2,000-3,000 for NMC), thermally safer, slightly heavier and cheaper. NMC (nickel manganese cobalt) is higher energy density and slightly better in extreme cold. Tesla Powerwall 3, FranklinWH, Enphase IQ Battery 5P all use LFP in 2026 products.
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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.