Battery Life Calculator - Calculate Battery Runtime & Capacity

Calculate Battery Life and Runtime for Any Device

Our comprehensive battery life calculator helps you determine how long your battery will last under specific load conditions. Whether you're designing electronics, planning power consumption, or simply curious about your device's battery life, this tool provides accurate runtime estimates based on battery capacity, current draw, and efficiency factors.

Key Features

Multiple Unit Support: Calculate with mAh, Ah, or Wh capacity units and mA or A current units
Efficiency Factor: Account for real-world battery efficiency and discharge characteristics
Voltage Consideration: Include battery voltage for accurate power calculations
Real-time Results: Get instant calculations as you type
Comprehensive Output: View runtime in hours, minutes, and seconds with power consumption details
Energy Calculations: See total energy capacity and power consumption in watts
Unit Conversions: Automatic conversion between different electrical units

How to Use the Battery Life Calculator

Enter Battery Capacity: Input your battery's capacity (e.g., 3000 mAh, 5 Ah, or 18.5 Wh)
Select Capacity Unit: Choose the appropriate unit (mAh, Ah, or Wh)
Enter Current Draw: Specify how much current your device draws (e.g., 500 mA, 2 A)
Select Current Unit: Choose between milliamperes (mA) or amperes (A)
Set Efficiency: Enter battery efficiency percentage (typically 80-95% for lithium batteries)
Specify Voltage: Enter the battery's nominal voltage (e.g., 3.7V for lithium-ion)
View Results: Get detailed runtime estimates and power consumption information

Understanding Battery Capacity Units

mAh (Milliampere-hour)

The most common unit for small batteries. Represents how much current (in milliamperes) a battery can supply for one hour. For example, a 3000 mAh battery can theoretically supply 3000 mA for 1 hour, or 1000 mA for 3 hours.

Ah (Ampere-hour)

Used for larger batteries like car batteries. 1 Ah = 1000 mAh. A 50 Ah car battery can supply 50 amperes for 1 hour, or 5 amperes for 10 hours.

Wh (Watt-hour)

Energy capacity that accounts for voltage. Calculated as Wh = Ah × Voltage. More accurate for comparing batteries with different voltages. For example, a 3.7V 5000 mAh battery has 18.5 Wh of energy.

Battery Efficiency Factors

Real-world battery performance is affected by several factors:

Temperature: Cold temperatures reduce battery capacity and efficiency
Discharge Rate: High current draws reduce effective capacity
Age and Cycles: Older batteries have reduced capacity
Chemistry: Different battery types have varying efficiency characteristics
Cutoff Voltage: Devices stop working before battery is completely empty

Common Battery Types and Characteristics

Lithium-ion (Li-ion)

Voltage: 3.7V nominal (3.0V - 4.2V range)
Efficiency: 85-95%
Common in: Smartphones, laptops, power tools

Lithium Polymer (Li-Po)

Voltage: 3.7V nominal
Efficiency: 85-95%
Common in: Drones, RC vehicles, some smartphones

Lead-Acid

Voltage: 12V nominal (10.5V - 14.4V range)
Efficiency: 70-85%
Common in: Cars, UPS systems, solar storage

Nickel-Metal Hydride (NiMH)

Voltage: 1.2V nominal
Efficiency: 80-90%
Common in: Rechargeable AA/AAA batteries, hybrid cars

Power Consumption and Energy Calculations

The calculator also provides power consumption information:

Power (W) = Current (A) × Voltage (V)
Energy (Wh) = Capacity (Ah) × Voltage (V)
Runtime (h) = Energy (Wh) ÷ Power (W)

Practical Applications

Electronics Design: Determine battery requirements for new devices
Power Management: Optimize device settings for longer battery life
Backup Planning: Calculate UPS runtime for critical systems
Solar Systems: Size battery banks for off-grid applications
Electric Vehicles: Estimate range based on power consumption
Portable Electronics: Choose appropriate battery capacity for projects

Tips for Accurate Calculations

Use Realistic Efficiency: Account for 10-20% efficiency loss in most applications
Consider Peak vs Average: Use average current draw, not peak consumption
Temperature Effects: Reduce capacity by 20-30% in cold environments
Safety Margins: Add 20-30% extra capacity for safety and aging
Multiple Loads: Sum all current draws when multiple devices share a battery

Frequently Asked Questions

What's the difference between mAh and Wh?

mAh (milliampere-hour) measures charge capacity, while Wh (watt-hour) measures energy capacity. Wh accounts for voltage: Wh = mAh × Voltage ÷ 1000. Wh is more accurate for comparing batteries with different voltages. For example, a 3.7V 3000 mAh battery has 11.1 Wh, while a 12V 1000 mAh battery has 12 Wh - more energy despite lower mAh.

Why is my actual battery life shorter than calculated?

Several factors reduce real-world battery life: temperature effects (cold reduces capacity), high discharge rates (reduces effective capacity), battery age and cycles, device cutoff voltage (stops before empty), and standby power consumption. The calculator uses ideal conditions, so add 20-30% safety margin for realistic estimates.

How do I find my device's current draw?

Check device specifications, use a multimeter to measure current, or look for power consumption ratings in watts and convert (Current = Power ÷ Voltage). For smartphones, typical usage is 200-500 mA, while heavy gaming might draw 1000+ mA. Many devices list power consumption in watts on their labels or manuals.

What efficiency percentage should I use?

For lithium-ion batteries, use 85-95% efficiency. Lead-acid batteries typically have 70-85% efficiency. NiMH batteries are around 80-90%. Consider your application: high-drain devices (power tools) use lower efficiency, while low-drain devices (clocks) can use higher efficiency values. When in doubt, use 85% for conservative estimates.

Can I use this calculator for any battery type?

Yes! The calculator works with any battery chemistry as long as you know the capacity, voltage, and efficiency. Just input the correct voltage for your battery type (3.7V for lithium, 1.2V for NiMH, 12V for lead-acid, etc.) and adjust the efficiency accordingly. The tool automatically handles unit conversions.

How accurate are the runtime calculations?

The calculations are mathematically accurate for the given inputs, but real-world results may vary due to temperature, discharge rate, battery age, and device efficiency. For planning purposes, the calculations are typically within 10-20% of actual performance. Always test with your specific setup for critical applications.

What if my device has variable power consumption?

Use the average power consumption over your typical usage period. For example, if a device uses 100 mA for 8 hours and 500 mA for 2 hours daily, the average is (100×8 + 500×2) ÷ 10 = 180 mA. For devices with very variable consumption, calculate for worst-case scenarios to ensure adequate battery life.