Battery Ghar Team · September 23, 2026 · Inverter Batteries
Backup time is one of the first questions buyers ask when choosing an inverter battery. A reliable estimate needs only a few inputs: the connected load, the battery capacity, the system voltage and a realistic allowance for losses.
Step 1: Add up the connected load
List every appliance that will run during a power cut and add their wattage. For example, four LED lights (4 × 10 W), two fans (2 × 75 W) and a Wi-Fi router (15 W) give a total load of 205 W.
Step 2: Note the battery capacity and system voltage
Inverter batteries are rated in ampere-hours (Ah). A single 12V, 150Ah battery stores roughly 12 × 150 = 1,800 watt-hours. A 24V system with two such batteries in series stores about 3,600 watt-hours.
Step 3: Apply efficiency and usable capacity
Inverters lose some energy in conversion, and lead-acid batteries should not be fully discharged. A practical factor of 0.7 to 0.8 covers inverter efficiency and usable depth of discharge.
The formula
Backup (hours) ≈ (Battery Ah × System Voltage × 0.75) ÷ Load (W)
Using the example above: (150 × 12 × 0.75) ÷ 205 ≈ 6.6 hours.
Factors that reduce real-world backup
- Battery age and state of health
- High ambient temperature
- Incomplete charging between outages
- Motor loads with high starting current
Share your load list and inverter rating with our team for an application-based recommendation on battery capacity and technology.