Battery Size Calculator

Determine the optimal battery size and capacity for your electronic projects based on voltage, current, and runtime requirements.

Calculate Your Battery Size Calculator

What is Battery Size?

Battery size refers to the capacity of a battery, typically measured in milliampere-hours (mAh) or ampere-hours (Ah). This capacity determines how long a battery can power a device before needing to be recharged. Choosing the right battery size is crucial for ensuring your electronic projects and devices operate for the required duration.

How to Calculate Battery Size

To calculate the required battery size (capacity) for a project, you need to know:

Current Draw: How much current your device requires, measured in milliamperes (mA)
Operating Time: How long you need the device to run on a single charge, measured in hours
Voltage: The voltage required by your device or circuit

The basic formula for calculating battery capacity is:

Battery Capacity (mAh) = Current Draw (mA) × Operating Time (hours)

For example, if your device draws 200mA and needs to run for 10 hours, you would need a battery with at least 2,000mAh capacity (200mA × 10h = 2,000mAh).

Adding a Safety Margin

It's recommended to add a 20-30% margin to your calculated capacity. This accounts for:

Battery capacity degradation over time
Variations in actual vs. rated capacity
Temperature effects on battery performance
Unexpected peaks in power consumption

Battery Capacity Units

mAh (milliampere-hours): Used for smaller batteries (phones, small electronics)
Ah (ampere-hours): Used for larger batteries (car batteries, solar systems)
Conversion: 1 Ah = 1,000 mAh

Battery Types

Lithium-Ion: High capacity, lightweight, 3.7V nominal
LiPo: Higher discharge rate, good for high-current applications
NiMH: 1.2V per cell, good for moderate current draw
Lead-Acid: 2V per cell, high capacity but heavy

Watt-Hours vs. Ampere-Hours

Sometimes battery capacity is expressed in watt-hours (Wh) rather than ampere-hours (Ah). Watt-hours take voltage into account, making it easier to compare batteries with different voltages:

Watt-hours (Wh) = Ampere-hours (Ah) × Voltage (V)

For example, a 3.7V battery with 2,000mAh capacity contains 7.4Wh of energy (2Ah × 3.7V = 7.4Wh).

Considerations When Choosing Battery Size

Physical Dimensions

Remember that higher capacity batteries are typically larger and heavier. Ensure your device has enough space for the battery you choose.

Temperature Effects

Battery performance decreases in cold temperatures. If your device operates in cold environments, consider selecting a larger battery capacity.

Discharge Rate

Some applications require high current bursts. Ensure your battery can handle the maximum current draw of your device (often specified as C-rating).

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Frequently Asked Questions

To determine the right battery size, you need to calculate your power requirements (voltage and current), the expected runtime, and any physical size constraints. Our Battery Size Calculator helps you determine the optimal battery capacity (in mAh or Ah) based on these factors.

mAh (milliampere-hours) and Ah (ampere-hours) are units that measure a battery's capacity. 1 Ah equals 1,000 mAh. Smaller batteries like those in phones use mAh ratings, while larger batteries like car batteries use Ah. Both represent how much current a battery can supply over time.

Voltage is critical in battery selection as your device requires a specific voltage to operate correctly. Using a battery with too low voltage won't power your device, while too high voltage might damage it. Sometimes batteries can be connected in series to increase voltage or in parallel to increase capacity.

To calculate runtime, divide the battery capacity (in mAh) by the current draw (in mA). For example, a 2000mAh battery powering a device that draws 500mA would last approximately 4 hours (2000 ÷ 500 = 4). Our calculator handles these calculations automatically.

Yes, temperature significantly affects battery performance. Batteries typically perform optimally at room temperature (20-25°C). Cold temperatures reduce capacity and discharge rate, while high temperatures increase self-discharge and can damage the battery. For outdoor or extreme environments, you may need to oversize your battery.

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