Battery Life Calculator
Estimated Runtime
What Is a Battery Life Calculator?
A battery life calculator is an online tool that estimates battery runtime based on power consumption.
Instead of manually calculating:
Battery Life (hours) = Battery Capacity (mAh) ÷ Load Current (mA)
the tool does the math for you. It also adjusts for real-world losses using a discharge efficiency percentage.
This makes the result more practical and closer to actual performance.
Why Battery Life Calculation Matters
Knowing battery runtime helps you:
- Design reliable electronic projects
- Size batteries for solar systems
- Estimate backup time for UPS systems
- Choose the right power bank
- Plan device usage during travel
For example:
If you have a 5000 mAh battery and your device draws 500 mA:
5000 ÷ 500 = 10 hours (ideal case)
But in real life, batteries are not 100% efficient. That is where discharge efficiency becomes important.
How the Battery Life Calculator Works
The calculator uses this formula:
Usable Capacity = Battery Capacity × (Efficiency ÷ 100)
Battery Life (Hours) = Usable Capacity ÷ Load Current
Let’s break this down.
1. Battery Capacity
You can enter capacity in:
- mAh (milliamp-hours)
- Ah (amp-hours)
The tool automatically converts Ah to mAh.
Example:
- 5 Ah = 5000 mAh
This ensures consistent calculation.
2. Load Current (Power Consumption)
This is how much current your device draws on average.
You can enter:
- mA
- A
The calculator converts amps to milliamps automatically.
Example:
- 0.5 A = 500 mA
3. Discharge Efficiency
Real batteries lose energy due to:
- Heat
- Internal resistance
- Age
- Temperature
The calculator defaults to 90% efficiency, which is common for Li-ion batteries under typical load.
If your battery is old or operating in harsh conditions, you may reduce this value.
Step-by-Step Example Calculation
Let’s say you enter:
- Battery Capacity: 5000 mAh
- Load Current: 500 mA
- Efficiency: 90%
Step 1: Calculate usable capacity
5000 × 0.90 = 4500 mAh
Step 2: Calculate runtime
4500 ÷ 500 = 9 hours
The calculator will display:
- 9.00 Hours
- 9 hours 0 minutes
- 4500 mAh effective
Simple and clear.
Features of the Battery Life Calculator Tool
✔ Automatic Unit Conversion
Switch between mAh and Ah, or mA and A, without manual conversion.
✔ Efficiency Adjustment
Accounts for real-world battery losses.
✔ Readable Time Output
Shows runtime in:
- Decimal hours
- Hours and minutes
✔ Instant Results
Click "Calculate Life" and get immediate output.
✔ Reset Function
Clear inputs and start fresh with one click.
Who Should Use This Tool?
This battery runtime calculator is useful for:
- Electronics students
- Engineers
- Solar installers
- DIY hobbyists
- RV owners
- Drone builders
- Power bank users
If your project runs on battery power, this tool helps you plan properly.
Real-World Factors That Affect Battery Life
Even the best calculator gives an estimate. Actual runtime depends on:
1. Temperature
Cold weather reduces battery efficiency.
2. Battery Age
Older batteries lose capacity over time.
3. Discharge Rate
High current draw reduces effective capacity.
4. Battery Chemistry
Li-ion, LiFePO4, and lead-acid batteries behave differently.
Common Battery Types and Their Typical Efficiency
Lithium-Ion (Li-ion)
- Typical efficiency: 85–95%
- Used in phones, laptops, power banks
LiFePO4
- High stability
- Good cycle life
- Efficiency often around 90–95%
Lead-Acid
- Lower usable capacity
- Efficiency may be 70–85%
Adjust the efficiency input based on your battery type for better estimates.
When to Use 100% Efficiency
Use 100% only for:
- Theoretical calculations
- Classroom learning
- Ideal lab conditions
For real-world applications, 85–95% gives more realistic results.
Limitations of the Battery Life Calculator
This calculator does not account for:
- Voltage changes during discharge
- Peukert’s Law (important for lead-acid batteries)
- Sudden load spikes
- Battery management system cutoffs
It assumes steady current draw.
For most small electronics projects, this assumption works well.