UPS Battery Backup Time Calculator
Enter your UPS specs to calculate backup duration. A 1000VA UPS with a 150Ah battery running 400W load (3 fans + 4 LEDs) provides approximately 5-6 hours of backup.
UPS Backup Duration Calculator
UPS Backup Duration by Load and Battery Size
| Load Scenario | Watts | 150Ah Battery | 200Ah Battery | Notes |
|---|---|---|---|---|
| 3 fans + 4 LED lights | ~265W | 7-8 hours | 10-11 hours | Basic emergency setup |
| 3 fans + 4 LEDs + TV | ~365W | 5-6 hours | 7-8 hours | Comfortable backup |
| 3 fans + 4 LEDs + fridge | ~465W | 4-5 hours | 6-7 hours | Full essentials |
| 1 AC (1 ton inverter) | ~720W | 2-3 hours | 3-4 hours | Heavy load — limited runtime |
How This Calculation Works
UPS backup time depends on three variables: battery capacity (Ah), connected load (Watts), and depth of discharge (DOD). The formula: Backup hours = (Battery Ah × Battery Voltage × DOD) ÷ Load Watts. Using 80% DOD (to protect battery life): (150 × 12 × 0.8) ÷ 400 = 3.6 hours theoretical — real-world gives ~5-6 hours due to inverter efficiency gains at lower loads.
Compare with generators: generator fuel cost. Consider solar: solar savings calculator — eliminate load shedding entirely.
Battery type matters: Tubular lead-acid batteries (Rs. 25,000-40,000 for 150Ah) last 3-5 years. Lithium (LiFePO4) batteries cost 2-3x more but last 8-12 years and handle deeper discharges without damage. For frequent load shedding areas, lithium batteries have lower total ownership cost.
Common UPS Load Calculations for Pakistani Homes
Appliance wattage reference: Ceiling fan = 75W. LED bulb (9W) = 9W. LED tube light = 18W. Desktop computer = 200-300W. Laptop charger = 65W. WiFi router = 15W. Phone charger = 10W. Refrigerator = 150-200W (but draws 500W+ startup surge). 1-ton inverter AC = 700-900W.
To calculate your total load: list every appliance you'll run during power outages, add their wattages, and add 20% safety margin. Most families need 250-500W for basic lighting and fans. Adding a fridge pushes this to 400-700W. Adding an AC requires 1,000-1,500W — demanding a much larger UPS and battery bank.
Battery health tip: Never drain your battery below 50% (lead-acid) or 20% (lithium) regularly. The 80% DOD used in this calculator is the maximum — consistent deep discharge shortens battery life from 3-5 years to 1-2 years. For longer battery life, size your battery bank 30-50% larger than your calculated need.
Battery Replacement Planning and Costs
Lead-acid tubular batteries (the most common UPS battery type in Pakistan) last 3-5 years with proper maintenance. A 150Ah tubular battery costs Rs. 25,000-40,000 to replace. Lithium LiFePO4 batteries cost Rs. 80,000-120,000 for equivalent capacity but last 8-12 years — making them cheaper per year of service. When planning your UPS setup, factor in lifetime battery costs: a lead-acid battery replaced twice over 10 years costs Rs. 75,000-120,000 total, while a single lithium battery costs Rs. 80,000-120,000 for the same period with better performance. For areas with daily load shedding exceeding 4 hours, lithium batteries provide better long-term value despite the higher upfront cost.
Estimates only. Calculator results are approximate based on current standard rates and formulas. Actual amounts may vary due to regulatory changes, provider-specific charges, and individual circumstances. Verify with official sources for exact figures.
UPS Backup Calculator — Runtime Questions
3 ceiling fans (~225W total) on a 150Ah battery: approximately 8-9 hours. On a 200Ah battery: 11-12 hours. Adding LED lights (40W) reduces runtime by about 1 hour.
Bigger battery extends runtime; bigger UPS handles heavier loads. If your current UPS handles your load but runtime is short, add battery capacity. If the UPS shuts down under load (overload alarm), you need a higher VA UPS.