Your inverter can last anywhere from 2 to 8 hours during a power cut, depending on the battery capacity, inverter voltage, depth of discharge (DoD), inverter efficiency, and the total load connected. In simple terms, the inverter alone does not provide backup—it relies entirely on the battery. The more energy stored in your battery and the fewer appliances you run, the longer the inverter will last.
In this guide, we’ll break down exactly how to calculate inverter backup time, step by step, with examples, tips, and practical tables so you can plan effectively.
Step 1: Know Your Battery Specs
To estimate inverter backup:
Battery Capacity (Ah): Typically 100Ah, 150Ah, 200Ah, or more.
Battery Voltage (V): Usually 12V, 24V, or 48V.
Depth of Discharge (DoD): Recommended 50–60% for tubular, 80–90% for lithium.
Inverter Efficiency: Usually 85–95%.
Example: A 12V, 150Ah battery has a total energy of 12 × 150 = 1,800 Wh. After accounting for DoD (50%) and inverter efficiency (85%), usable energy = 1,800 × 0.5 × 0.85 ≈ 765 Wh.
Step 2: Calculate Total Load
Add up the wattage of all connected appliances:
4 LED bulbs (10W each) = 40W
1 Fan (75W) = 75W
1 TV (120W) = 120W
Total Load = 235W
Step 3: Apply the Backup Formula
Backup Time (hours) = Usable Battery Energy (Wh) / Total Load (W)
Using our example:
Backup Time = 765 / 235 ≈ 3.25 hours
✅ This means your inverter will run these appliances for about 3 hours during a power cut.
Step 4: How to Increase Backup Duration
Add more batteries in parallel to increase total Ah.
Reduce load by switching off non-essential appliances.
Use lithium batteries for higher DoD and more usable energy.
Optimize inverter size to prevent efficiency losses.
Maintain batteries regularly for maximum output.
Step 5: Real-World Factors That Affect Backup
Startup Surges: Fans and pumps can draw 2–3× rated power temporarily.
Battery Age: Older batteries deliver less energy.
Temperature: High ambient heat reduces battery efficiency.
Voltage Drops: Voltage decreases as the battery discharges, slightly affecting inverter performance.
Step 6: Quick Reference Table
| Battery Specs | Load (Watts) | DoD | Efficiency | Backup Time (Hours) |
|---|---|---|---|---|
| 12V, 150Ah | 235 | 50% | 85% | 3.25 |
| 12V, 150Ah | 150 | 50% | 85% | 5.08 |
| 12V, 300Ah | 235 | 50% | 85% | 6.5 |
| 24V, 200Ah | 400 | 50% | 85% | 5.1 |
Step 7: Tips for Maximizing Inverter Backup
Prioritize essential appliances during power cuts.
Avoid frequent deep discharges.
Add extra battery capacity for longer outages.
Keep batteries cool and ventilated.
Monitor inverter and battery health regularly.
Conclusion
In summary, how long your inverter lasts during a power cut depends on your battery’s capacity, DoD, inverter efficiency, and connected load. Using the simple calculation formula and considering real-world factors like surges, battery age, and temperature, you can accurately plan your backup. Whether using tubular or lithium batteries, understanding your load and maintaining your system ensures reliable power whenever the grid goes down. With proper planning, an inverter can provide anywhere from a couple of hours to several hours of backup during outages in 2026.