Inverter Battery Backup Time Calculator
How long will an inverter battery run your load? Peukert-corrected backup hours for Indian tubular banks.
The eternal Indian power-cut question: how many hours will the inverter last? Convert your load (fans ≈ 75 W, LED lights ≈ 9 W, fridge ≈ 150 W avg) to amps at 12 V (watts ÷ 12 ÷ inverter efficiency ≈ watts ÷ 10), enter it as load current, and Peukert's law gives the honest backup time — always less than the brochure math.
Peukert's law: t = H·(C/IH)^k. At 20 A, your 100 Ah battery behaves like a 71 Ah one — lead-acid loses usable capacity fast under heavy loads, which is why inverter banks are oversized and why lithium (k ≈ 1.03) delivers nearly full capacity at any rate.
Engineering estimate from published standards and typical equipment data. Site conditions, equipment datasheets and measured data govern the real result — confirm with a qualified engineer.
Use the free Inverter Battery Backup Time Calculator online — How long will an inverter battery run your load? Peukert-corrected backup hours for Indian tubular banks. Runs instantly in your browser: no signup, no upload, mobile-friendly.
About Inverter Battery Backup Time Calculator
The eternal Indian power-cut question: how many hours will the inverter last? Convert your load (fans ≈ 75 W, LED lights ≈ 9 W, fridge ≈ 150 W avg) to amps at 12 V (watts ÷ 12 ÷ inverter efficiency ≈ watts ÷ 10), enter it as load current, and Peukert's law gives the honest backup time — always less than the brochure math.
How to use Inverter Battery Backup Time Calculator
- 1Enter the rated capacity and its hour basis (usually C20).
- 2Set the Peukert exponent for your battery construction (help text guides).
- 3Enter your actual load current and read the honest runtime and effective capacity.
Why use Inverter Battery Backup Time Calculator?
- ✓The 1897 law that explains why your '100 Ah' battery isn't
- ✓Construction-specific exponents: flooded, AGM, gel, lithium
- ✓Honest runtime at YOUR load, not the 20-hour lab rate
- ✓Explains inverter-bank sizing in one screen
Frequently asked questions
Why does my battery last much less than the Ah rating suggests?+
Peukert's law: lead-acid capacity shrinks as discharge current rises. A 150 Ah C20 battery delivers its rating only at 7.5 A; at 30 A it behaves like ~100 Ah. The rating wasn't a lie — it was measured at a gentler rate than your inverter draws.
What is a typical Peukert exponent?+
Flooded lead-acid 1.25–1.35, AGM 1.10–1.25, gel 1.20–1.30, lithium (LFP) 1.02–1.05 — effectively immune. Higher k means faster capacity collapse under load. Quality datasheets let you derive k from the C20/C10/C5 ratings.
How should I size a battery bank for an inverter?+
Compute your load current (watts ÷ battery voltage ÷ inverter efficiency), apply Peukert to get effective capacity, then size so the load stays near the rating's hour basis and within your DoD budget (50% for lead-acid). This is why serious inverter banks look 'oversized' — they're sized honestly.
Does Peukert's law apply to lithium batteries?+
Barely — LFP holds nearly full capacity from C/20 to 1C (k ≈ 1.03). That's a hidden economic edge: a 100 Ah LFP delivers ~95+ Ah under heavy load where a 100 Ah lead-acid delivers ~65 Ah, narrowing the real price-per-usable-Ah gap dramatically.
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