Understanding Battery Life Calculation

Battery life refers to the duration a device can operate before its battery requires recharging. Calculating this effectively requires understanding the relationship between capacity, consumption, and efficiency factors.

Key Concepts & Conversion

Before using the calculator, it is helpful to understand the units involved:

• Amp-hour (Ah): A unit of electric charge. It represents the amount of energy charge in a battery that will allow one ampere of current to flow for one hour.
• Milliamp-hour (mAh): This is the unit most commonly used for small electronics. 1 Ah = 1000 mAh.
• Watt-hour to Amp-hour: If you know the energy in Watt-hours (Wh) and the nominal voltage (V), you can convert it using this formula:

$Ah = \frac{Wh}{V}$

The Battery Life Formula

While no battery lasts forever, you can estimate the approximate runtime using this standard formula:

$Battery Life = \frac{Capacity}{Consumption} \times (1 - Discharge Safety)$

Where:

• Capacity (Ah or mAh): The total energy storage of the battery. This is usually printed on the battery's label.
• Consumption (A or mA): The average current draw of your electronic device. Note: Ensure Capacity and Consumption use the same unit scale (e.g., both in mA).
• Discharge Safety (%): The percentage of battery capacity that is never used to prevent damage. (Commonly 20% or 0.2 for Lead Acid; Li-ion batteries can often go lower, but a safety margin is always recommended).

Factors Affecting Accuracy

Calculated results are estimates. Real-world performance depends on several variables:

• Battery Condition: Age and cycle count (older batteries hold less charge).
• Temperature: Extreme cold or heat significantly reduces efficiency.
• Discharge Rate: Drawing power too quickly (Peukert's Law) can reduce effective capacity.

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Reference: Typical Battery Capacities (mAh)

The following table provides estimated capacities for common battery types to help you estimate if you don't have the exact data sheet.

Battery Size	Chemistry	Estimated Capacity (mAh)	Notes
AAA	Alkaline	1200	Standard remote batteries
	NiMH	800 – 1000	Rechargeable
AA	Alkaline	2700	Standard household use
	Lithium (Rechargeable)	3000	High drain devices
	NiMH	1700 – 2900
C	Alkaline	8000	Medium drain
	NiMH	4500 – 6000
D	Alkaline	12000	High capacity flashlights
	NiMH	2200 – 12000	Wide variance in quality
	Lithium-Primary (3.6V)	19000	Industrial use
9V (PP3)	Alkaline	565	Smoke detectors
	Lithium-Primary	1200	Long-life applications
	NiMH	175 – 300
6V Lantern	Alkaline	26000	Heavy duty lighting
CR2032	Lithium-Primary (3V)	240	Coin cell (BIOS, watches)
CR2016	Lithium-Primary (3V)	90	Thinner coin cell
1/10 D	Lithium-Primary (3.6V)	1000	Specialized industrial
4 Farad Cap	Capacitor	~1 mAh	Equivalent @ 1mA drain/1V drop