How to Calculate Inverter Battery Backup?
Buying an inverter battery (like Exide or Luminous) is expensive, so you need to know exactly how long it will support your appliances during a power cut. The formula for backup time is technical but easy to understand.
The Formula
Backup Time = (Battery Ah × Voltage × Efficiency) / Total Load
Typically, Lead-acid batteries have an efficiency of about 80% (0.8 power factor).
Example Calculation
Suppose you have a 150 Ah battery (12V) and you are running:
- 2 Ceiling Fans (75W x 2 = 150W)
- 2 LED Bulbs (10W x 2 = 20W)
- Total Load = 170 Watts
Result: (150 x 12 x 0.8) / 170 = ~8.4 Hours.