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UPS Battery Backup Calculator
How long will a 200Ah battery really run 3 fans? Pick your battery, tick what you actually run during loadshedding, and get an honest answer in hours — plus what recharging will cost you.
Add at least one appliance above — and make sure the battery size is a number above 0.
Estimates only. Real backup time varies with battery age, how deeply the battery has been drained in the past, inverter quality and your actual load. The recharge cost uses the per-unit price you enter above — an editable estimate, not an official electricity tariff.
Tool 12 — About this tool
What this UPS battery backup calculator does
When the power goes in Pakistan, one question decides your evening: how long will the battery last? Most answers online quietly assume you can use 100% of the battery — you cannot, not without destroying it. This calculator does the maths the honest way. Pick your battery size, choose tubular or lithium, tick the fans, lights and screens you actually run, and it shows your real backup time, your total load, and what it costs in electricity units to recharge the battery afterwards.
The formula, in plain words
Usable energy (Wh) = 12V × battery size (Ah) × usable % × 0.85 inverter efficiency
Backup hours = usable Wh ÷ total load (W)
The usable % is the part nobody tells you: a tubular lead-acid battery should only be drained to about half (50% usable) or it dies young, while a lithium battery gives you about 90%. The 0.85 covers what the inverter itself wastes turning battery power into the power your fans use.
The question everyone asks: 200Ah, 3 fans
Three ceiling fans draw about 225W together. A 200Ah tubular battery holds 12 × 200 × 50% × 0.85 = 1,020 usable watt-hours, so 1,020 ÷ 225 = about 4.5 hours. The same battery in lithium gives 1,836 usable watt-hours — about 8.2 hours. Try it above: the calculator opens with exactly this setup.
How to use it — 3 steps
- Pick your battery size and type. If your size is not listed, tap Custom and type it in — the number is printed on the battery itself.
- Use the + and − steppers for everything you run during a cut. Wattages are pre-filled with typical Pakistani home values, but every wattage is editable if your appliance label says different.
- Read your backup time, then check the recharge rows: how many units (kWh) refilling the battery takes, and what that costs at your own per-unit price.
Who it is for
Anyone in a loadshedding area deciding whether their current UPS setup is enough, anyone shopping for a battery who wants to size it before spending, and anyone whose electricity bill jumped and wants to know what each power cut is quietly costing them in recharge units.
Honest limitations
This is an estimate, not a promise. Real backup varies with battery age — a three-year-old tubular battery holds noticeably less than a new one — with how deeply it has been drained in the past, with inverter quality, and with your true load. Fridges cycle on and off rather than drawing full power constantly, so a fridge on the list makes the estimate cautious, not exact. The recharge cost is only as good as the per-unit price you type in; it is an editable estimate, not an official tariff.
FAQ
UPS Battery Backup Calculator — common questions
How long will a 200Ah battery run 3 fans?
About 4.5 hours on a tubular (lead-acid) battery, and about 8.2 hours on lithium. Three ceiling fans draw roughly 225W. A 200Ah tubular battery only gives you half its charge safely — 12V × 200Ah × 50% × 0.85 inverter efficiency = 1,020 usable watt-hours, and 1,020 ÷ 225W ≈ 4.5 hours. Lithium lets you use 90% of the charge, which is why it lasts close to twice as long on the same Ah rating.
Why is my real backup time shorter than the estimate?
Usually the battery, not the maths. Batteries lose capacity as they age, and tubular batteries that have been drained too deep, too often, lose it faster. Inverter quality matters too, and small things add up: fans on full speed draw more than fans on medium, and an old fridge can pull well above its label when its compressor starts. Treat the calculator's number as a healthy-battery estimate — if yours is years old, expect less.
How much does it cost to recharge the battery after a power cut?
Refilling a fully drained 200Ah battery takes about 3 units (kWh) from the grid once charging losses are counted — roughly Rs 150 at Rs 50 per unit. Smaller cuts cost proportionally less, because you only repay the energy you used. The price per unit is editable in the calculator: type the rate from your own electricity bill for a closer figure. It is an estimate for planning, not an official tariff.
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