Electrical calculator
Battery Life Calculator
Estimate how long a battery will last under a given load.
About the battery life calculator
The battery life calculator estimates how long a battery will last under a given load, accounting for efficiency losses.
How to use this calculator
- 1
Enter battery capacity
Enter the battery capacity in mAh.
- 2
Enter load current
Enter the device's current draw in mA.
- 3
Set efficiency
Enter efficiency factor (typically 70-90% for real-world use).
How the calculation works
Runtime = (capacity × efficiency) ÷ current. Real-world efficiency is typically 70–90%.
Example: 3000 mAh battery at 500 mA, 80% efficiency ≈ 4.8 hours.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about battery life calculator
How accurate is the battery life calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.