How Much Backup Will Your Battery Really Give? Use the Free Calculator Built on My Lab Tests
By Kunwer Sachdev — mentor at Su-vastika, founder of Su-Kam
Every week, someone asks me the same question: "How many hours of backup will my battery give?" And every week, somewhere in India, a family discovers that the answer printed in a brochure has very little to do with what happens in their home during a power cut.
So I built the answer — properly. A free calculator that works from my own laboratory discharge tests, not from formula arithmetic.
⚡ Try the Free Backup Calculator →
This is not theory — this is the actual test
A 12V/150Ah tubular battery, a home inverter, and a bulb load board, logged minute by minute to the 10.5V cutoff:
The discharge test in progress — real bulbs, real battery, real clock. Watch the test video and full data here →
What the battery actually delivers
Measured in my lab: the same 150Ah battery shrinks as the load grows. The harder you pull, the less it gives.
What the calculator tells you that no brochure will
The number BIS requires on every nameplate — because VA has no fixed relationship to watts in Indian inverter standards. Buy by watts, not VA.
12V, 24V, 48V, 96V or 120V — with the exact battery Ah for your backup target, from 30 minutes to 8 hours.
Interpolated from measured discharge curves — and it knows that refrigerators, ACs and geysers cycle on and off, so real backup runs longer than rated-watt math suggests.
Including how often you will top up distilled water. A lightly loaded battery may need water once a year; an overworked one, every month. The water level is your battery telling you the truth.
Where the data comes from
The engine behind the calculator is a set of minute-by-minute discharge logs — 150Ah and 200Ah tubular batteries, bulb loads from 400W to 1400W, run to the 10.5V cutoff. I published the complete dataset, charts and the test video openly, so anyone can verify the numbers: read the full test data article.
I built this as an independent tool on my publication, inverterindia.com — no affiliate links, no sponsorships, no bias. It recommends no brand, including ours. It simply tells you the truth about what batteries do under load, because after thirty years in this industry I believe the customer deserves the real number before they spend their money.
🔍 Calculate your real backup time →
— Kunwer Sachdev, the Inverter Man of India. Calculator, methodology and test data © 2026 Kunwer Sachdev, first published on inverterindia.com, June 2026. All rights reserved.