Battery Backup Time Calculator

About Battery Backup Time Calculator

The Battery Backup Time Calculator helps you determine how long a battery will power your devices or appliances. This free online tool calculates runtime based on battery voltage, capacity (Ah), load power (W), and system efficiency. Perfect for UPS systems, inverters, solar installations, and backup power planning.

Battery Backup Time Formula

Backup Time (hours) = (Voltage × Capacity × Efficiency%) / Load Power

Where Voltage is in Volts (V), Capacity in Ampere-hours (Ah), Efficiency as percentage, and Load Power in Watts (W).

Common Applications

✓ UPS Systems: Calculate backup time for computers, routers, and network equipment
✓ Home Inverters: Estimate runtime for lights, fans, and appliances during power outages
✓ Solar Systems: Plan battery bank size for off-grid and hybrid solar installations
✓ RV & Marine: Determine how long batteries will last for recreational vehicles and boats
✓ Emergency Backup: Size batteries for emergency lighting and critical equipment

Efficiency Considerations

Inverter Efficiency: Typical inverters operate at 85-95% efficiency. Lower quality inverters may be 70-80%.

Battery Type: Lead acid batteries are typically 80% efficient, while lithium batteries can reach 90-95%.

Depth of Discharge: Lead acid batteries should only be discharged to 50%, while lithium can safely go to 80-90%.

Temperature: Cold temperatures reduce battery capacity and efficiency significantly.

How to Use This Calculator

Enter Battery Voltage: Common values are 12V, 24V, or 48V
Enter Battery Capacity: Found on battery label in Ah (Ampere-hours)
Enter Load Power: Total wattage of devices you want to power
Adjust Efficiency: Use 85% as default, or adjust based on your system
View Results: Get instant backup time in hours and minutes

Example Calculations

Example 1: Router Backup

Battery: 12V 7Ah | Load: 30W | Efficiency: 85%

Result: 2.38 hours (2h 23m)

Example 2: Home Inverter

Battery: 12V 100Ah | Load: 150W | Efficiency: 85%

Result: 6.8 hours (6h 48m)

Example 3: Solar System

Battery: 24V 200Ah | Load: 500W | Efficiency: 90%

Result: 8.64 hours (8h 38m)