Battery Capacity Runtime Calculator
Estimate ideal runtime from battery capacity and load current, determine the capacity needed for a target operating time, or calculate the allowable average load current from a known battery. Use this simple capacity-current-time model for early power budgeting and battery sizing. For Active, Idle, and Sleep load profiles, use the duty-cycle battery runtime calculator.
Engineering tool
Battery Capacity Runtime Calculator
Estimate simple battery runtime, required capacity, or allowable load current with automatic engineering-unit conversion.
Primary Result
10 h
Result console
- Runtime
- 10h
- Minutes
- 600min
- Seconds
- 36,000s
- Days
- 0.416667days
- Battery capacity
- 3Ah
- Load current
- 300mA
Battery status
Good
Formula: Runtime = Capacity / Current
Scientific notation: 1.0000e+1 h
The ideal runtime supports a typical working-day duty cycle. Add capacity margin for real battery behavior.
Formula reference
Battery Runtime Formulas
Use amp-hours, amperes, and hours as the consistent base units.
Runtime = Capacity / CurrentCapacity = Runtime × CurrentCurrent = Capacity / RuntimeVariable definitions
- Capacity
- available battery charge in amp-hours
- Current
- average load current in amperes
- Runtime
- ideal operating time in hours
Worked Examples
Calculate Runtime
3000 mAh / 300 mA = 10 hours.
Required Capacity
500 mA × 12 hours = 6000 mAh.
Load Current
10 Ah / 20 hours = 0.5 A, or 500 mA.
Engineering Notes
- Battery runtime is an ideal estimate based on average current and nominal capacity.
- Actual runtime depends on battery chemistry and its discharge curve.
- Temperature affects usable capacity and voltage performance.
- Battery aging reduces available capacity over repeated cycles and calendar time.
- High discharge rates can reduce effective runtime and increase voltage sag.
- Always include safety margin for conversion losses, peak loads, cutoff voltage, and product reserve.
Support reference
FAQ
What does the battery capacity runtime calculator solve?
It solves simple capacity, current, and runtime relationships. Divide capacity in amp-hours by average load current in amperes to estimate ideal runtime in hours.
Why is actual runtime shorter?
Usable capacity falls with conversion loss, battery cutoff voltage, peak loads, self-discharge, aging, temperature, and discharge-rate effects.
Does temperature affect battery life?
Yes. Low temperature commonly reduces available capacity and voltage performance, while sustained high temperature accelerates battery aging.
Can I use this for lithium batteries?
Yes, for an initial capacity-based estimate. Verify the cell discharge curve, protection cutoff, load profile, and manufacturer ratings for the actual design.
What units are supported?
Capacity supports mAh and Ah; current supports µA, mA, and A; runtime supports seconds, minutes, hours, and days.
When should I use the duty cycle battery runtime calculator?
Use the duty-cycle calculator when the load has Active, Idle, and Sleep states. This page is for a simple average-current runtime estimate.
Documentation
Related Engineering Resources
Guides and lookup references linked to this tool.
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