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. The formula for backup time is simple but technical.
The Formula
Backup Time = (Battery Ah × Voltage × Efficiency) / Total Load in Watts
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.
Use this calculator to plan whether you need a single battery (12V) or a double battery system (24V) for your home.