Battery Runtime Calculator
Calculate how long any battery lasts with a given load.
About the Battery Runtime Calculator
Built for Pakistani users, the Battery Runtime Calculator turns a fiddly manual calculation into a one-glance result you can trust for planning and everyday decisions.
A UPS keeps the essentials running through load-shedding — but only if it is sized correctly for your load and backup needs. This Battery Runtime Calculator sizes a UPS system from the appliances you need to power and the backup hours you want.
The calculation combines the load wattage and the desired backup time to arrive at the battery capacity and UPS rating required, using the standard relationship between watts, battery volts and amp-hours.
The most common UPS mistake in Pakistan is buying on the VA rating without checking the battery: two 'same size' UPS units can differ hugely in backup time because battery capacity varies. This tool sizes the battery, which is what actually determines runtime.
Remember the 50% rule for lead-acid batteries: plan for discharge down to about half capacity to protect battery life. The calculator's result reflects usable capacity, so the backup time it shows is realistic.
For the most accurate outcome from the Battery Runtime Calculator, keep the editable rates and defaults up to date with current figures before reading the result.
How to size a UPS
- 1
Enter the load — the total wattage of fans, lights and other essentials.
- 2
Enter the backup hours you want during an outage.
- 3
Read the UPS rating and battery capacity required, updated live.
Frequently Asked Questions
What depth of discharge should I use?
For lead-acid batteries, discharge no more than 80% (ideally 50%) to protect lifespan. Lithium batteries tolerate deeper discharge.
How many watts does a typical UPS load need?
Two fans (~150 W total), three LED bulbs (~25 W) and a TV (~100 W) add up to roughly 275 W. A 1–1.5 kVA UPS covers this with room to spare.
Why does my UPS backup time drop after a year?
Lead-acid batteries lose capacity with age and deep discharges. Keeping discharge above 50% and avoiding heat extends battery life significantly.