Battery Runtime Calculator
Calculate how long a battery will power your devices. Enter battery capacity and load to estimate runtime for UPS, power stations, and backup systems.
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How to Use This Calculator
Calculate how long a battery will power your devices:
- Enter the battery capacity in amp-hours (Ah) or milliamp-hours (mAh).
- Input the load current in amps or milliamps that your device draws.
- Optionally adjust the efficiency factor (typically 80-90% for real-world use).
- Click 'Calculate' to see estimated runtime.
Why This Matters
Whether you're sizing a UPS for computer backup, planning a camping trip with battery power, or designing a solar battery system, knowing how long power will last is essential. Battery runtime depends on capacity, load, and efficiency - and the relationship isn't always intuitive. Temperature, discharge rate, and battery age all affect actual runtime. This calculator gives you a realistic estimate for planning purposes.
- Size UPS systems for adequate computer backup time
- Plan portable power for camping, RVing, or emergencies
- Design battery backup systems for solar installations
- Compare battery options based on runtime needs
- Estimate how long devices run on battery power
Worked Examples
UPS Backup
1500VA UPS with 100Ah battery bank powering a 500W computer setup.
Camping Power Station
500Wh portable power station running a 50W CPAP machine overnight.
Phone Charging
10,000mAh power bank charging a phone with 4,000mAh battery.
Common Mistakes to Avoid
- Using 100% of battery capacity in calculations - real-world efficiency is typically 80-90%.
- Ignoring that discharge rate affects capacity - faster discharge = less usable capacity.
- Not accounting for inverter losses when powering AC devices from DC batteries.
- Forgetting that cold temperatures significantly reduce battery capacity.
- Draining batteries to 0% - many batteries shouldn't discharge below 20-50% for longevity.