Battery Lifetime Calculator
Estimate how long your battery can power a device using battery capacity, voltage, average current draw, and real-world derating factors.
How this battery runtime calculator works
This calculator estimates battery life in hours and days based on how much charge your battery stores and how quickly your device consumes that charge. It also includes two practical adjustments: usable capacity and efficiency.
In real projects, you rarely get the full rated battery capacity. Temperature, discharge rate, aging, voltage cutoffs, and regulator losses all reduce actual runtime. That’s why this model includes derating values so your estimate is more realistic.
Formula used
Effective Capacity (mAh) = Battery Capacity × (Usable % / 100) × (Efficiency % / 100)
Average Current (mA) = Current Draw × (Duty Cycle % / 100)
Runtime (hours) = Effective Capacity / Average Current
How to use the calculator
- Battery Capacity (mAh): enter your battery’s rated capacity.
- Battery Voltage (V): used for energy and average power reporting (Wh, W).
- Current Draw (mA): average current while active.
- Duty Cycle (%): if your device is active only part of the time, enter that percentage.
- Usable Capacity (%): account for cutoff limits and aging (common range: 70–95%).
- System Efficiency (%): include losses from converters, wiring, and regulation.
Example scenario
Portable sensor node
Suppose you have a 3000 mAh lithium-ion battery, your sensor averages 120 mA, duty cycle is 60%, usable capacity is 85%, and power-path efficiency is 92%.
- Effective capacity = 3000 × 0.85 × 0.92 = 2346 mAh
- Average current = 120 × 0.60 = 72 mA
- Estimated runtime = 2346 ÷ 72 ≈ 32.6 hours
That’s about 1 day and 8 hours before recharge (under stable operating conditions).
What affects real battery life most?
- Temperature: cold environments can dramatically reduce available capacity.
- Peak current pulses: high bursts may trigger early voltage sag/cutoff.
- Battery chemistry: Li-ion, LiFePO4, NiMH, and lead-acid behave differently.
- Aging and cycle count: older batteries can lose significant capacity.
- Load profile: sleep-heavy designs often outlast steady loads of similar average current.
Tips to increase battery lifetime
Hardware strategies
- Use high-efficiency DC-DC converters near your normal load range.
- Reduce quiescent current in regulators and sensors.
- Size wiring and traces to minimize voltage drop.
Firmware strategies
- Increase deep-sleep time and reduce wake duration.
- Batch wireless transmissions instead of always-on radio.
- Lower sampling rates where acceptable.
Quick FAQ
Can I convert mAh directly to hours?
Yes, if current draw is known and conditions are stable. Runtime in hours is approximately mAh divided by mA. This calculator improves that estimate with duty cycle and derating.
Why include voltage if runtime uses mAh and mA?
Voltage helps compute energy in watt-hours and average power in watts, which is useful when comparing different battery packs or power architectures.
Is this exact?
It’s an engineering estimate. For final design decisions, validate with bench testing across temperature, load pulses, and end-of-life battery conditions.