UPS Battery Backup Calculator
Calculate how long your UPS or inverter battery will last during load-shedding — enter load watts and battery Ah/voltage to get backup time instantly.
About the UPS Battery Backup Calculator
Load-shedding makes 'how long will my UPS last?' an everyday question in Pakistan. This calculator answers it properly: enter your running load in watts and your battery bank (Ah, voltage, number of batteries) and it computes realistic backup time using inverter efficiency and a safe 50% depth of discharge for lead-acid and tubular batteries.
Not sure of your load? Use the quick-add chips — ceiling fan 75W, LED bulb 10W, TV 100W, fridge 150W, laptop 60W — to build it up appliance by appliance. The formula is transparent: Ah × V × batteries × 85% inverter efficiency × 50% usable depth ÷ load.
A comparison table shows the backup time of common Pakistani setups (100Ah, 150Ah, 200Ah single batteries and 24V series banks) at your load, so you can see exactly what upgrading your battery would buy you before spending the money.
How to Use the UPS Battery Backup Calculator
- 1Build your load with the appliance chips or type the total watts.
- 2Enter your battery capacity (Ah), voltage and how many batteries you have.
- 3Adjust inverter efficiency if you know it (85% is typical).
- 4Read the backup time, and compare common battery setups in the table.
Frequently Asked Questions
How long will a 150Ah battery run 2 fans and 4 LED bulbs?
That's about 190W of load. A single 12V 150Ah battery holds 150 × 12 × 0.85 × 0.5 ≈ 765Wh usable, giving roughly 4 hours of backup — enough for a typical load-shedding spell.
Why does the calculator only use 50% of the battery capacity?
Discharging lead-acid and tubular batteries below ~50% drastically shortens their life — batteries that are routinely run flat can die within a year. Lithium batteries tolerate ~80%; adjust mentally if you have one.
Can I run a fridge on a UPS during load-shedding?
Yes, but note that a fridge's compressor draws a surge (3–5× its running watts) at startup, so your inverter must handle it. Its ~150W average also roughly halves the backup time of a typical single-battery UPS.
Does adding a second battery double my backup time?
A second battery in parallel (same 12V) doubles Ah and roughly doubles backup. Two batteries in series make a 24V bank for bigger inverters — same energy, but the inverter runs more efficiently at higher voltage.
Why is my real backup time less than calculated?
Battery age is the usual culprit — capacity fades 30–50% over a battery's life. Heat, undercharging (frequent outages never let it fill) and wiring losses also cut real-world backup below the math.