Calculate your battery backup time
Calculate how long your battery will last during power outages Works with lead-acid, lithium-ion, UPS, solar, and car batteries
Battery Parameters
Backup Time Results
Backup Time
Usable Capacity
Load Current
Recommended DoD
Common Backup Times
| Battery Capacity | 100W Load | 200W Load | 500W Load | 1000W Load |
|---|---|---|---|---|
| 50Ah (12V) | 5.4 hours | 2.7 hours | 1.1 hours | 0.5 hours |
| 100Ah (12V) | 10.8 hours | 5.4 hours | 2.2 hours | 1.1 hours |
| 150Ah (12V) | 16.2 hours | 8.1 hours | 3.2 hours | 1.6 hours |
| 200Ah (12V) | 21.6 hours | 10.8 hours | 4.3 hours | 2.2 hours |
| 100Ah (24V) | 21.6 hours | 10.8 hours | 4.3 hours | 2.2 hours |
Backup Time Formula
To calculate battery backup time:
Where:
- Battery Capacity in Amp-hours (Ah)
- Voltage in Volts (V)
- DoD = Depth of Discharge (80% for lithium, 50% for lead-acid)
- Efficiency = Inverter efficiency (typically 85-95%)
- Load Power in Watts (W)
Battery Types Comparison
Lithium-ion
Depth of Discharge: 80-90%
Efficiency: 95-98%
Life Cycles: 2000-5000
AGM
Depth of Discharge: 50-60%
Efficiency: 85-90%
Life Cycles: 500-800
Flooded
Depth of Discharge: 40-50%
Efficiency: 70-85%
Life Cycles: 300-500
Lithium batteries provide more usable capacity and longer lifespan, but at a higher initial cost.
Tips to Extend Backup Time
Maximize your battery backup with these strategies:
- Use energy-efficient appliances (LED lights, inverter ACs)
- Prioritize essential loads only during outages
- Maintain batteries properly – clean terminals, check water levels
- Keep batteries at optimal temperature (20-25°C)
- Use pure sine wave inverters for better efficiency
- Consider adding more battery capacity
Reducing load by 50% can more than double your backup time!
Battery Backup FAQs
- Determine your battery capacity in Amp-hours (Ah)
- Note the battery voltage (usually 12V, 24V, or 48V)
- Calculate total watt-hours: Capacity (Ah) × Voltage (V)
- Apply Depth of Discharge (DoD): 80% for lithium, 50% for lead-acid
- Multiply by inverter efficiency (typically 85-95%)
- Divide by your load in watts
Example: 100Ah 12V battery with 200W load:
(100 × 12 × 0.8 × 0.9) ÷ 200 = 4.32 hours
- 100W load: ≈21.6 hours
- 200W load: ≈10.8 hours
- 500W load: ≈4.3 hours
- 1000W load: ≈2.2 hours
For a 24V system, backup times would be approximately double these values for the same load.
- 100W load: ≈32.4 hours
- 200W load: ≈16.2 hours
- 500W load: ≈6.5 hours
- 1000W load: ≈3.2 hours
Calculation: (150Ah × 24V × 0.8 DoD × 0.9 efficiency) = 2592 Wh
2592 Wh ÷ Load (W) = Backup hours
- Battery capacity (Ah)
- Battery voltage (12V, 24V, etc.)
- Battery type (lithium lasts longer than lead-acid)
- Total power consumption of your devices
- Inverter efficiency
- Battery age and temperature
Use our calculator above to get an accurate estimate for your specific setup.
- Connected load
- Battery capacity (varies by model)
- Battery age
Typical backup times at full load:
- Entry-level: 5-10 minutes
- Mid-range: 10-20 minutes
- Extended battery models: 30-60+ minutes
For computer backup (300W load), expect 15-30 minutes on most models.
- Calculate watt-hours: Capacity (Ah) × Voltage (V)
- Apply 80-90% Depth of Discharge (DoD)
- Multiply by 95% inverter efficiency
- Divide by load in watts
Example: 100Ah 12V lithium battery with 200W load:
(100 × 12 × 0.85 × 0.95) ÷ 200 = 4.845 hours
- LED lights (10W): ≈30 hours
- Router + modem (20W): ≈15 hours
- Laptop (50W): ≈6 hours
- TV (100W): ≈3 hours
- Mini fridge (150W): ≈2 hours
Important considerations:
- Car batteries are not designed for deep discharge
- Limit discharge to 20-30% to avoid damage
- Use a pure sine wave inverter for sensitive electronics
- Never run your battery completely flat