Battery Life Calculator
Estimate how long a battery lasts given its capacity and the device's power draw.
About the Battery Life Calculator
Whether you are comparing options or just need a quick check, the Battery Life Calculator delivers an accurate result instantly, with every input editable so you can model your own scenario.
Battery capacity, charging time and backup duration are the numbers behind every phone, UPS and solar installation in Pakistan. This Battery Life Calculator computes one of these battery figures so your power planning is based on real numbers.
The calculation uses the standard relationships between battery capacity (Ah or Wh), device load, and time — the same math used to size UPS and solar batteries.
With load-shedding still part of life in many areas, battery backup planning matters: how long will a UPS keep a fan and lights running, or how big a battery does a solar system need for overnight power? This calculator answers those questions.
Remember that batteries should not be discharged fully — lead-acid batteries last far longer when kept above 50% charge. Factor that reserve into your planning.
Bookmark the Battery Life Calculator for the next time you need it, and explore the rest of GuruAlpha's 1,200+ calculators for related everyday maths.
How to use the battery calculator
- 1
Enter the battery capacity and the load it powers.
- 2
Adjust the efficiency or discharge limit if the tool asks.
- 3
Read the backup time or required capacity, updated live.
Frequently Asked Questions
How is battery runtime calculated?
Runtime = capacity ÷ draw. A 5,000 mAh battery feeding a 500 mA device lasts ~10 hours. Real life is a bit lower due to voltage conversion losses.
How long will a UPS battery last?
Divide the battery's usable capacity (in Wh) by the load (in watts). A 150 Ah, 12 V battery holds 1,800 Wh; powering 200 W of fans and lights gives roughly 7–8 hours of backup at normal discharge.
Should I discharge my battery fully?
No — deep discharge damages lead-acid batteries and cuts their life sharply. Keep discharge above 50% for lead-acid; lithium batteries tolerate deeper discharge but still last longer with a reserve.