Battery Life Calculator
Estimate battery runtime for your electronics, solar storage, or mobile devices. Convert between capacity, power consumption, and real-world operating hours.
Technical Overview
The Runtime Formula
Battery runtime is calculated by dividing total capacity by the current consumption draw, and multiplying by the efficiency derating factor:
If load is given in Watts, Current is calculated as $I = P / V$.
Why Efficiency Matters
In electronics, energy conversion is never 100% efficient. Factors reducing runtime include:
- • Voltage Regulators: Buck/boost converters lose 5% to 15% as heat.
- • Inverters: Converting DC battery power to AC wall power generally operates at 85% to 90% efficiency.
- • Peukert's Law: Discharging a battery quickly reduces its effective total capacity.
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Frequently Asked Questions
How is battery life calculated?
The basic theoretical formula for battery runtime is: Battery Capacity divided by Device Consumption. For example, a 2000 mAh battery powering a 500 mA device will theoretically last 4 hours (2000 / 500 = 4).
Why do you include an efficiency factor?
In the real world, batteries never achieve 100% of their theoretical runtime. Energy is lost as heat due to internal resistance, voltage regulators, inverter conversion losses, and aging chemistry. A standard recommendation is to multiply theoretical runtime by 0.85 (85% efficiency) for a realistic estimate.
What is the difference between mAh and Ah?
Both measure electric charge capacity. 'mAh' stands for milliampere-hour, commonly used for smaller batteries like smartphones, AA batteries, and USB power banks. 'Ah' stands for ampere-hour, used for larger systems like automotive batteries, RV setups, and solar storage. 1 Ah equals 1,000 mAh.
Why is battery voltage required when measuring load in Watts?
Watts measure total electrical power ($P = V \times I$), while mAh/Ah measure electric charge...
What is the C-rate or discharge rate?
The C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means the discharge current will drain the entire battery in 1 hour. Discharging at very high rates (greater than 1C) significantly reduces actual battery capacity due to Peukert's Law.