How to Calculate Battery Runtime
Learn how to calculate how long your battery or solar generator will last. Use our interactive calculator to get instant results.
Battery Runtime Calculator
Enter your battery's capacity in Watt-hours (Wh)
Enter your device's power consumption in Watts
Or select a common device:
Results
Runtime assumes 85% efficiency and full battery charge. Actual results vary based on temperature, battery age, and device usage patterns.
The Formula
Battery Capacity
Measured in Watt-hours (Wh). Check your battery label.
Inverter Efficiency
Usually 85% (0.85). Higher for pure sine wave inverters.
Device Power Draw
Check your device's label or use our common device guide.
Common Device Power Guide
| Device | Average Watts | Daily Hours | Daily Wh | 2000Wh Runtime |
|---|---|---|---|---|
| Refrigerator | 150W | 24h | 3600Wh | 11.3h |
| LED TV (50") | 100W | 4h | 400Wh | 17h |
| Laptop | 65W | 6h | 390Wh | 26h |
| Phone Charger | 10W | 2h | 20Wh | 170h |
| CPAP Machine | 60W | 8h | 480Wh | 28h |
| Wi-Fi Router | 20W | 24h | 480Wh | 85h |
| LED Lights (4x) | 30W | 6h | 180Wh | 56h |
Tips to Extend Battery Runtime
Use DC power directly
Many devices can run on 12V DC, bypassing the inverter and saving 15% efficiency loss.
Turn off unused devices
Even in standby mode, devices draw power. Unplug or turn off when not needed.
Use energy-efficient appliances
LED lights and Energy Star appliances use significantly less power.
Keep batteries warm
Batteries lose capacity in cold weather. Keep them above 50°F for best performance.
Frequently Asked Questions
Why do I get less runtime than expected?
Batteries have a usable capacity (usually 80-85% of rated capacity) due to inverter inefficiency, temperature, and depth of discharge limits.
How do I check my device power draw?
Check the device label or user manual. You can also use a Kill-A-Watt meter for real-time measurements.
Can I run multiple devices at once?
Yes, but total wattage must be under the inverter's rated output. Runtime = Capacity ÷ Total Watts.
Ready to Calculate Your Runtime?
Use our full battery runtime calculator for more detailed results.