Power method: Runtime (hours) = (Battery Capacity (mAh) × Battery Voltage (V)) ÷ Power (W) ÷ 1000
Note: Real-world battery life is affected by temperature, age, discharge rate, and battery chemistry.
Battery Life Calculator — Complete Guide to Estimating Battery Runtime
Understanding how long your battery will last is essential for designing electronics, planning IoT projects, selecting portable devices, and managing power consumption. This comprehensive guide explains everything you need to know about battery life calculation, from basic formulas to advanced considerations.
📐 Understanding Battery Capacity and Consumption
Battery capacity is measured in milliampere-hours (mAh) or ampere-hours (Ah). It represents the total charge a battery can deliver. A 2000 mAh battery can theoretically provide 2000 mA (2A) for 1 hour, or 100 mA for 20 hours.
Current consumption is measured in milliamps (mA) or amps (A). It represents the amount of current a device draws from the battery. Lower current draw means longer battery life.
Power consumption is measured in watts (W) and is calculated as Voltage × Current. For battery life calculations, you can use either current or power values.
🔢 Core Battery Life Formulas
Using Current (mA): Runtime (hours) = Battery Capacity (mAh) ÷ Current Draw (mA)
Using Power (W) and Voltage (V): Runtime (hours) = (Capacity (mAh) × Voltage (V)) ÷ (Power (W) × 1000)
Example: 2000 mAh battery, 100 mA draw → 2000 ÷ 100 = 20 hours
📊 Battery Life Reference Table
Here's a quick reference for common battery capacities and current draws:
| Battery Capacity (mAh) | Current Draw (mA) | Runtime (Hours) | Runtime (Days) | Common Device |
|---|---|---|---|---|
| 500 | 10 | 50 | 2.08 | IoT sensor |
| 1,000 | 50 | 20 | 0.83 | Bluetooth tracker |
| 2,000 | 100 | 20 | 0.83 | Smartphone (standby) |
| 2,500 | 200 | 12.5 | 0.52 | Portable speaker |
| 3,000 | 500 | 6 | 0.25 | Tablet (active) |
| 5,000 | 1,000 | 5 | 0.21 | Power bank (charging) |
| 10,000 | 100 | 100 | 4.17 | IoT gateway |
| 20,000 | 500 | 40 | 1.67 | Laptop (standby) |
| 50,000 | 1,000 | 50 | 2.08 | Electric bike battery |
| 100,000 | 5,000 | 20 | 0.83 | Electric scooter |
🔄 Real-World Battery Life Examples
Smartphone Battery Life
Example: 4000 mAh battery, 200 mA standby draw → 20 hours standby. 1000 mA screen-on draw → 4 hours screen time.
Formula: 4000 ÷ 200 = 20h | 4000 ÷ 1000 = 4h
IoT Sensor Battery Life
Example: 2000 mAh battery, 5 mA active draw, 0.1 mA sleep (95% sleep) → ~20,000 hours (~2.3 years).
Formula: Effective current = (5×0.05 + 0.1×0.95) = 0.345 mA | 2000 ÷ 0.345 = 5,797 hours
Wireless Earbuds
Example: 50 mAh per earbud, 10 mA draw → 5 hours playtime. Charging case extends to 20+ hours.
Formula: 50 ÷ 10 = 5 hours
Laptop Battery
Example: 60 Wh battery (≈16,200 mAh at 3.7V), 15W consumption → 4 hours runtime.
Formula: (16200 × 3.7) ÷ (15 × 1000) = 4.0 hours
🔋 Factors That Affect Real Battery Life
The calculated battery life is theoretical. Real-world battery life is affected by:
- Battery chemistry: Li-ion, LiPo, NiMH, and Alkaline have different discharge characteristics
- Temperature: Cold temperatures reduce battery capacity and increase internal resistance
- Battery age: As batteries age, their capacity decreases (typically 20-30% over 2-3 years)
- Discharge rate: High current draws reduce effective capacity (Peukert's Law)
- Depth of discharge: Deep discharges reduce battery lifespan
- Device efficiency: Voltage regulators, power supplies, and firmware efficiency affect actual consumption
- Self-discharge: Batteries lose charge even when not in use (typically 1-5% per month)
- Battery cutoff voltage: Devices stop working before battery is fully drained
📡 Peukert's Law: High Current Draw Impact
Peukert's Law describes how battery capacity decreases at higher discharge rates. For example, a 2000 mAh battery rated at 0.2C (400 mA) may only deliver 1800 mAh at 1C (2000 mA).
Practical impact: If your device draws high current, expect 10-20% less battery life than the simple calculation suggests.
Peukert's Law formula: Cactual = Crated × (Irated ÷ Iactual)^(n-1) where n ≈ 1.1-1.3 for most batteries.
📊 Battery Life by Device Type
Smartphone
2,000-5,000 mAh1-3 days typical use
Laptop
30-100 Wh4-12 hours typical
Earbuds
30-80 mAh4-8 hours playtime
IoT Sensor
500-2,000 mAhMonths to years
E-Bike
10-20 Ah (10,000-20,000 mAh)20-60 miles range
Smartwatch
200-500 mAh1-3 days typical
🔄 How to Use This Battery Life Calculator
- Enter battery capacity in milliampere-hours (mAh). Check your battery's label or datasheet.
- Enter current consumption in milliamps (mA). Measure or estimate your device's current draw.
- Alternatively, use power method — enter power in watts (W) and battery voltage (V).
- Click "Calculate Battery Life" to see runtime in hours, minutes, and days.
- Use the reference table for quick estimates without calculations.
❓ Frequently Asked Questions
A: Divide battery capacity (mAh) by current draw (mA). For example, 2000 mAh ÷ 100 mA = 20 hours.
A: Runtime (hours) = (Capacity (mAh) × Voltage (V)) ÷ (Power (W) × 1000). For example, (2000 mAh × 3.7V) ÷ (1.5W × 1000) = 4.93 hours.
A: Real-world factors like temperature, battery age, discharge rate, and device efficiency reduce actual runtime. Expect 10-30% less than theoretical calculations.
A: Cold temperatures reduce battery capacity and increase internal resistance. Li-ion batteries lose 20-30% capacity at 0°C compared to 25°C.
A: Peukert's Law describes how battery capacity decreases at higher discharge rates. A battery rated at 2000 mAh may only deliver 1800 mAh at high current draws.
A: Use a multimeter in series with the battery. For accurate results, measure at the device's operating voltage. Many devices have varying current draw depending on usage.
A: mAh (milliampere-hours) measures charge capacity at a given voltage. Wh (watt-hours) measures energy. Wh = (mAh × V) ÷ 1000. Wh is more accurate for comparing batteries with different voltages.
A: Runtime depends on current draw. At 500 mA, it lasts 10 hours. At 100 mA, it lasts 50 hours. Use our calculator to find your specific runtime.
📈 Common Battery Life Myths
- Myth: "A 2000 mAh battery always lasts 2000 mAh" — Fact: Effective capacity depends on discharge rate, temperature, and battery age.
- Myth: "Higher mAh always means longer battery life" — Fact: Higher capacity generally means longer life, but device consumption and battery chemistry also matter.
- Myth: "Battery life is linear" — Fact: Battery discharge is not perfectly linear; voltage drops near the end of discharge.
- Myth: "Calculated battery life is exact" — Fact: Calculated battery life is theoretical; real-world runtime varies significantly.
📡 Pro Tip: Extending Battery Life
To maximize your battery life:
- Reduce current draw: Use low-power components, dim displays, reduce processor speed
- Use sleep modes: Put devices in low-power sleep mode when not in use
- Optimize firmware: Efficient code reduces CPU time and power consumption
- Manage temperature: Keep batteries at room temperature (20-25°C) for optimal performance
- Choose efficient converters: Use high-efficiency voltage regulators to minimize power loss
- Monitor battery health: Replace batteries that have significantly degraded
🔋 Battery Chemistries Comparison
Li-ion
Voltage: 3.6-3.7V
Capacity: High
Self-discharge: 2-3%/month
Pros: High energy density, no memory effect
Cons: Requires protection circuit, aging
LiPo
Voltage: 3.7V
Capacity: Very high
Self-discharge: 2-3%/month
Pros: High energy density, flexible shape
Cons: Sensitive to overcharge, swelling risk
NiMH
Voltage: 1.2V
Capacity: Medium
Self-discharge: 20-30%/month
Pros: Durable, good for high current
Cons: Memory effect, lower energy density
Alkaline
Voltage: 1.5V
Capacity: Low-Medium
Self-discharge: 1-2%/year
Pros: Cheap, widely available
Cons: Non-rechargeable, high internal resistance
📈 Future of Battery Technology
Battery technology continues to evolve, offering longer life and faster charging:
- Solid-state batteries: Higher energy density, faster charging, safer
- Lithium-sulfur: 2-3× higher energy density than Li-ion
- Graphene batteries: Ultra-fast charging, long cycle life
- Sodium-ion: Cheaper, sustainable alternative to lithium
- Wireless charging: Inductive and resonant charging becoming mainstream
- Energy harvesting: Solar, thermal, and kinetic energy to extend battery life
🎓 Educational Resources and Further Reading
- Explore our complete suite of calculators
- Power Consumption Calculator
- Charging Time Calculator
- Energy Cost Calculator
- Ohm's Law Calculator
- Read our blog for more tech tips
Last updated: January 2026. Our Battery Life Calculator is regularly reviewed for accuracy and performance.