Battery Life Calculator
Calculate how long a battery will last based on its capacity and the load current. Estimate battery runtime for your devices.
Battery efficiency (default: 100%)
How to Use This Calculator
- Enter the battery capacity in mAh (found on the battery label or specifications).
- Enter the load current in mA (the current your device draws).
- Adjust the efficiency percentage if needed (default: 100% for ideal conditions).
- The calculator displays the estimated battery life in hours and minutes.
Battery Life Formula
Battery life is calculated from capacity, load, and efficiency:
Example: 3000mAh battery with 500mA load at 90% efficiency: Life = (3000 / 500) × 0.9 = 6 × 0.9 = 5.4 hours = 5 hours 24 minutes.
Full Description
Calculating battery life helps you estimate how long a device will run on a single charge, plan battery replacements, and select appropriate batteries for your applications. Battery life depends on three main factors: battery capacity (how much charge it stores), load current (how much current the device draws), and battery efficiency (how much energy is actually usable).
In ideal conditions, battery life is simply capacity divided by load current. However, real-world factors reduce actual runtime: internal resistance causes voltage drop, batteries lose capacity with age, and efficiency losses occur during discharge. Using an efficiency factor (typically 80-95%) provides more realistic estimates. Higher load currents also reduce usable capacity in some battery types.
This calculator helps you estimate battery runtime. Enter capacity, load current, and efficiency, and it calculates the expected battery life. Use it when selecting batteries, planning device runtime, or understanding power consumption. Remember that actual battery life varies with usage patterns, temperature, and battery condition.
Frequently Asked Questions
How do I calculate battery life?
Battery life = (Battery capacity in mAh) / (Load current in mA) × (Efficiency / 100). For example, a 3000mAh battery with 500mA load at 100% efficiency: Life = 3000 / 500 = 6 hours.
What is battery efficiency?
Battery efficiency accounts for energy losses due to internal resistance, self-discharge, and voltage drop. Most batteries are 80-95% efficient. The calculator defaults to 100% for ideal conditions, but you can adjust for more realistic estimates.
How does load current affect battery life?
Higher load current drains the battery faster, reducing runtime. Battery life is inversely proportional to load current. Doubling the load current halves the battery life. Some batteries also show lower capacity at higher discharge rates.
Why is my actual battery life shorter than calculated?
Actual battery life is often shorter due to: voltage drop under load, battery aging, temperature effects, self-discharge, and efficiency losses. Use a lower efficiency percentage (80-90%) for more realistic estimates.