What is the UPS Battery Backup Calculator?
How long will your UPS keep the fans and lights running during load-shedding? Enter the total load in watts, battery capacity (Ah), voltage and the number of batteries, choose lead-acid or lithium, and get the estimated backup time.
It also tells you what battery capacity you need for 4 hours of backup and a suggested UPS/inverter size in VA.
How to use the UPS Battery Backup Calculator
- Add up the watts of everything you want to run (see the table).
- Enter battery Ah, voltage, number and type.
- Read the backup time.
Formula
Backup (hours) = battery Ah × voltage × number of batteries × depth of discharge × inverter efficiency ÷ load (W). Example: one 150 Ah 12 V tubular battery with a 400 W load: 150 × 12 × 0.5 × 0.85 ÷ 400 ≈ 1.9 hours.
Make your battery last longer
- Use DC inverter fans and LED lights.
- Do not discharge lead-acid batteries below 50% regularly.
- Keep battery water levels topped up (tubular batteries).
Frequently asked questions
Why only 50% for lead-acid?
Deep discharges shorten lead-acid battery life; lithium batteries can safely use 80–90%.
What UPS size do I need?
Roughly load ÷ 0.7 in VA – a 400 W load needs about a 600 VA UPS.
Does battery age matter?
Yes, old batteries hold much less charge than their rating.
Is it free?
Yes.
This ups battery backup calculator is 100% free, needs no signup and works on phones, tablets and computers. Your data is processed in your browser and never uploaded.
Last updated: · By NodifyTech