Solar Battery Backup Calculator (2026)

Enter your AC, extra load and the backup hours you want, and get the battery bank size in kWh and Ah — with LiFePO4 and lead-acid options costed side by side for Indian homes.

Overnight power-cut sizing LiFePO4 vs lead-acid Free · no sign-up

Step 1 — Your AC

Tonnage

Star rating

We use the AC's average overnight draw — an inverter AC holding a set temperature uses far less than its nameplate watts.

Step 2 — Other load on backup

Fans, lights, Wi-Fi, fridge

200 W

A typical bedroom set is 150–300 W.

Step 3 — Backup hours needed

Hours of power cut to cover

8 h

Summer power cuts in much of India cluster overnight — 8 hours covers 10 PM to 6 AM.

Advanced

LiFePO4 price (₹/kWh)

Lead-acid price (₹/kWh)

Battery bank voltage Ah figures below are quoted at this bank voltage. AC-capable inverters are usually 24 V or 48 V.

How the sizing works

Your AC's average running draw = cooling capacity ÷ ISEER for its star rating — an inverter AC holding a set temperature overnight draws well under its nameplate watts. Energy needed = (AC draw + other load) × backup hours ÷ 90% inverter efficiency. The battery bank is then sized so that energy fits inside the chemistry's usable depth of discharge: LiFePO4 can safely give back ~80% of its rated kWh, flooded lead-acid only ~50% — which is why the same backup needs a much bigger (and heavier) lead-acid bank. Prices are 2026 India market ballparks for the battery alone, excluding the inverter/PCU. LiFePO4 also lasts 4–6× more cycles, so its per-cycle cost is usually lower despite the sticker premium.

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