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Battery Life Calculator

Free Battery Life Calculator for computer & it. Free online tool with accurate results using verified formulas.

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Computer & IT

Battery Life Calculator

Calculate battery runtime from capacity, current draw, duty cycle, and efficiency. Compare usage scenarios and find the right battery size for your device.

Last updated: December 2025

Calculator

Adjust values & calculate
5000 mAh
250 mA
5 mA
3.7V
100%
85%
Estimated Battery Life
17.0 hours
17.0 hours | 0.7 days | 250.0 mA avg draw
Usable Capacity
4250 mAh
Energy Stored
15.72 Wh
Power Draw
925.0 mW

Duty Cycle Scenarios

Always Active
17.0 hours(250 mA)
Current Settings
17.0 hours(250.0 mA)
50% Duty Cycle
1.4 days(127.5 mA)
25% Duty Cycle
2.7 days(66.3 mA)
10% Duty Cycle
6.0 days(29.5 mA)
Sleep Only
5.1 weeks(5 mA)

Battery Size for Target Duration

8h runtime2353 mAh needed
1d runtime7059 mAh needed
2d runtime14118 mAh needed
1wk runtime49412 mAh needed
1mo runtime211765 mAh needed
Your Result
Battery Life: 17.0 hours | Effective Current: 250.0 mA | Power: 0.925 W
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Understand the Math

Formula

Battery Life (hours) = (Capacity x Efficiency) / Effective Current

Where Capacity is battery capacity in mAh, Efficiency is the percentage of capacity that is usable (accounting for internal losses), and Effective Current is the weighted average current draw considering active current, sleep current, and duty cycle. Effective Current = Active Current x Duty Cycle + Sleep Current x (1 - Duty Cycle).

Last reviewed: December 2025

Worked Examples

Example 1: IoT Sensor Node Battery Life

A wireless sensor has a 3000 mAh battery at 3.7V. It draws 150 mA when active and 3 mA in sleep mode. The duty cycle is 10% (active 6 minutes per hour). Efficiency is 85%.
Solution:
Effective current = 150 x 0.10 + 3 x 0.90 = 15 + 2.7 = 17.7 mA Usable capacity = 3000 x 0.85 = 2550 mAh Battery life = 2550 / 17.7 = 144.1 hours = 6.0 days Energy stored = 3000 x 3.7 / 1000 = 11.1 Wh Power consumption = 17.7 x 3.7 = 65.5 mW
Result: Battery life: 144.1 hours (6.0 days) with 17.7 mA effective draw. The 10% duty cycle extends life 7x compared to always-on (33.6h).

Example 2: Smartphone Battery Estimation

A smartphone has a 4500 mAh battery at 3.85V. Average screen-on current is 350 mA. With 4 hours screen time and 20 hours standby at 15 mA, what is the daily battery usage?
Solution:
Screen-on: 350 mA x 4h = 1400 mAh Standby: 15 mA x 20h = 300 mAh Total daily: 1400 + 300 = 1700 mAh Usable capacity (90%): 4500 x 0.90 = 4050 mAh Days per charge: 4050 / 1700 = 2.38 days
Result: The phone lasts approximately 2.4 days per charge with this usage pattern, consuming 1700 mAh or 37.8% of usable capacity daily.
Expert Insights

Background & Theory

The Battery Life Calculator applies the following established principles and formulas. Computers represent all information using binary, a base-2 number system consisting solely of the digits 0 and 1, each called a bit. Because long binary strings are unwieldy, programmers routinely use octal (base 8) and hexadecimal (base 16) as compact shorthand. Converting between bases follows a consistent algorithm: divide the source number repeatedly by the target base, collecting remainders in reverse order. Hexadecimal digits A through F represent the values 10 through 15, allowing a single character to encode four binary bits, making it the preferred notation for memory addresses, color codes, and bytecode. Bitwise operations manipulate individual bits within integers. AND produces a 1 only when both input bits are 1, making it useful for masking. OR produces a 1 when either bit is 1 and is used for combining flags. XOR flips bits that differ, enabling simple toggle logic and efficient swap algorithms. NOT inverts every bit (one's complement), while left and right shifts multiply or divide by powers of two in constant time. Data storage units ascend in binary multiples of 1024: 8 bits form one byte, 1024 bytes form one kibibyte (KiB), 1024 KiB form one mebibyte (MiB), and so forth. Hard-drive manufacturers historically use decimal prefixes (1 KB = 1000 bytes), creating the persistent confusion between binary and decimal interpretations of the same label. The IEC standardized the binary prefixes KiB, MiB, GiB, and TiB in 1998 to resolve this ambiguity. Network bandwidth is measured in bits per second (bps), most commonly megabits per second (Mbps) or gigabits per second (Gbps). A 100 Mbps connection transfers 100 million bits every second, equating to roughly 12.5 megabytes per second. IP subnet masks define network boundaries; CIDR notation appends a prefix length (e.g., /24) to an address, indicating how many leading bits are fixed. A /24 subnet contains 256 addresses with 254 usable hosts. Algorithm efficiency is described using Big-O notation, which characterises the worst-case growth of time or space relative to input size. O(1) is constant, O(log n) is logarithmic (binary search), O(n) is linear, and O(nยฒ) is quadratic. Cryptographic hash functions like SHA-256 produce a fixed 256-bit (32-byte) digest regardless of input length. File compression algorithms exploit statistical redundancy to reduce storage footprint, and compression ratio equals the original file size divided by the compressed size.

History

The history behind the Battery Life Calculator traces back through the following developments. The conceptual foundation of modern computing traces back to Charles Babbage, whose Analytical Engine design of 1837 introduced the idea of a general-purpose mechanical computer with separate storage and processing units, including what he called the Store and the Mill. Ada Lovelace wrote what many consider the first algorithm intended for machine execution while annotating a translation of Luigi Menabrea's account of Babbage's work, also recognising the machine's potential to manipulate symbols beyond mere numbers. George Boole published "The Laws of Thought" in 1854, formalising a two-valued algebra of logic that would later map perfectly to electrical circuits. It remained largely a mathematical curiosity until Claude Shannon's landmark 1937 master's thesis demonstrated that Boolean algebra could describe switching circuits, laying the theoretical groundwork for all digital electronics. Shannon's 1948 paper "A Mathematical Theory of Communication" defined the bit as the fundamental unit of information and established information theory as a rigorous discipline. The same year, the transistor was invented at Bell Labs by Bardeen, Brattain, and Shockley, eventually replacing vacuum tubes and enabling miniaturisation at scale. ENIAC, completed in 1945, was one of the first general-purpose electronic computers, occupying 1800 square feet and consuming 150 kilowatts of power while performing roughly 5000 additions per second. The ASCII standard was ratified in 1963, assigning 7-bit codes to 128 characters and enabling interoperability between computers from different manufacturers. Through the 1970s, the microprocessor consolidated an entire CPU onto a single chip; Intel's 4004 in 1971 marked the beginning of this trend. The Apple II launched in 1977 and the IBM PC in 1981 brought computing to homes and offices, triggering a mass-market software industry. Tim Berners-Lee proposed the World Wide Web in 1989 and launched the first website in 1991 at CERN, transforming the internet from an academic and military network into a global information infrastructure. Mobile computing accelerated through the 2000s with smartphones integrating powerful processors, wireless networking, and GPS into pocket-sized devices, extending computation into every facet of daily life and cementing TCP/IP as the universal communications fabric.

Key Features

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  • Convert between all storage units (bits, bytes, KB, MB, GB, TB, PB) using both decimal (SI) and binary (IEC) standards to resolve the common confusion between manufacturers and operating systems.
  • Compute pixel density (PPI) from screen resolution and physical dimensions, helping users evaluate display sharpness for monitors, phones, and tablets.
  • Estimate server rack capacity and RAID configuration outcomes (RAID 0, 1, 5, 6, 10) including usable storage, fault tolerance, and rebuild time.
  • Calculate battery life from mAh capacity and device power consumption in milliwatts, with adjustments for screen-on time, background drain, and charge cycle degradation.
  • Generate subnet masks, network addresses, broadcast addresses, and host ranges from CIDR notation, supporting both IPv4 and IPv6 planning.
  • Quantify the effect of network latency and jitter on real-time applications such as VoIP, gaming, and video conferencing using round-trip time thresholds.
  • Estimate monthly cloud infrastructure costs for compute instances, object storage, data egress, and managed databases across major providers.

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Frequently Asked Questions

Battery life is calculated by dividing the battery capacity in milliamp-hours (mAh) by the average current draw in milliamps (mA). The formula is: Battery Life (hours) = Battery Capacity (mAh) / Average Current Draw (mA). For example, a 3000 mAh battery powering a device that draws 200 mA will last approximately 15 hours (3000 / 200 = 15). However, this is a theoretical maximum. Real-world battery life is typically 80-90% of this value due to internal resistance, voltage regulation inefficiencies, and the fact that batteries cannot be fully discharged to zero without damage. Battery Life Calculator accounts for these factors through the efficiency percentage input.
Battery capacity measured in milliamp-hours (mAh) represents the total amount of electrical charge a battery can store and deliver. One mAh means the battery can supply 1 milliamp of current for 1 hour, or equivalently 2 milliamps for 30 minutes. Common battery capacities include 2000-5000 mAh for smartphones, 3000-8000 mAh for tablets, 40000-100000 mAh for laptops (expressed as 40-100 Wh), and 100-500 mAh for IoT sensors. The capacity rating is measured at a specific discharge rate, and actual usable capacity can vary depending on how fast you draw current. Higher discharge rates typically yield slightly lower effective capacity due to internal resistance losses and heat generation.
Duty cycle is the percentage of time a device is in its active or high-power state versus its sleep or low-power state. A 50% duty cycle means the device is active half the time and sleeping the other half. This dramatically affects battery life because sleep mode typically consumes 10-100 times less current than active mode. For example, a sensor that draws 100 mA when active and 5 mA when sleeping with a 10% duty cycle has an effective average current of (100 x 0.10) + (5 x 0.90) = 14.5 mA, extending battery life nearly 7 times compared to always-on operation. Optimizing duty cycle is the single most effective strategy for extending battery life in IoT and embedded devices.
Battery efficiency accounts for energy losses that prevent you from using 100% of the rated capacity. These losses come from several sources. Internal resistance converts some energy to heat during discharge, typically wasting 5-15% of capacity. Voltage regulation circuits in your device waste additional energy converting the battery voltage to the levels needed by various components. Self-discharge causes batteries to lose charge even when not in use, at rates of 1-5% per month for lithium batteries. Temperature effects can reduce effective capacity by 10-30% in cold conditions. Finally, most devices shut down before the battery is fully depleted to prevent damage. A realistic efficiency value is 80-90% for lithium-ion batteries in normal conditions.
Several factors cause real-world battery life to fall short of calculated estimates. Temperature is a major factor, with lithium batteries losing 10-20% capacity at freezing temperatures and degrading faster in high heat above 40 degrees Celsius. Battery aging reduces capacity by approximately 20% after 500 charge cycles. Peak current demands during processor-intensive tasks or radio transmissions cause voltage drops that waste energy through internal resistance. Background processes and wake events increase average current above expected levels. Power management circuitry such as voltage regulators typically operates at 85-95% efficiency. Parasitic drain from protection circuits and voltage monitoring adds a few microamps of constant draw. Account for these factors by using a conservative efficiency value of 70-80% for realistic estimates.
Different battery chemistries offer distinct advantages for various applications. Lithium-ion (Li-ion) batteries at 3.7V nominal offer high energy density of 150-250 Wh/kg and 500-1000 charge cycles, making them ideal for phones and laptops. Lithium polymer (LiPo) batteries have similar chemistry but can be manufactured in thin, flexible shapes. Lithium iron phosphate (LiFePO4) batteries offer 2000+ cycles but lower energy density, good for solar applications. Alkaline AA batteries provide 1.5V with 2500-3000 mAh capacity for low-drain consumer devices. Lithium primary cells like CR2032 coin cells offer 230 mAh at 3V with 10-year shelf life for IoT sensors and wearables. Nickel-metal hydride (NiMH) rechargeable AAs provide 1.2V with 2000-2800 mAh for moderate drain applications.
Educational Note: This calculator is provided for educational and informational purposes. Results are based on the formulas and inputs provided. Always verify important calculations independently. NovaCalculator processes calculator inputs client-side; optional analytics follow visitor consent settings. ยฉ 2024โ€“2026 NovaCalculator.

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Formula

Battery Life (hours) = (Capacity x Efficiency) / Effective Current

Where Capacity is battery capacity in mAh, Efficiency is the percentage of capacity that is usable (accounting for internal losses), and Effective Current is the weighted average current draw considering active current, sleep current, and duty cycle. Effective Current = Active Current x Duty Cycle + Sleep Current x (1 - Duty Cycle).

Worked Examples

Example 1: IoT Sensor Node Battery Life

Problem: A wireless sensor has a 3000 mAh battery at 3.7V. It draws 150 mA when active and 3 mA in sleep mode. The duty cycle is 10% (active 6 minutes per hour). Efficiency is 85%.

Solution: Effective current = 150 x 0.10 + 3 x 0.90 = 15 + 2.7 = 17.7 mA\nUsable capacity = 3000 x 0.85 = 2550 mAh\nBattery life = 2550 / 17.7 = 144.1 hours = 6.0 days\nEnergy stored = 3000 x 3.7 / 1000 = 11.1 Wh\nPower consumption = 17.7 x 3.7 = 65.5 mW

Result: Battery life: 144.1 hours (6.0 days) with 17.7 mA effective draw. The 10% duty cycle extends life 7x compared to always-on (33.6h).

Example 2: Smartphone Battery Estimation

Problem: A smartphone has a 4500 mAh battery at 3.85V. Average screen-on current is 350 mA. With 4 hours screen time and 20 hours standby at 15 mA, what is the daily battery usage?

Solution: Screen-on: 350 mA x 4h = 1400 mAh\nStandby: 15 mA x 20h = 300 mAh\nTotal daily: 1400 + 300 = 1700 mAh\nUsable capacity (90%): 4500 x 0.90 = 4050 mAh\nDays per charge: 4050 / 1700 = 2.38 days

Result: The phone lasts approximately 2.4 days per charge with this usage pattern, consuming 1700 mAh or 37.8% of usable capacity daily.

Frequently Asked Questions

How is battery life calculated?

Battery life is calculated by dividing the battery capacity in milliamp-hours (mAh) by the average current draw in milliamps (mA). The formula is: Battery Life (hours) = Battery Capacity (mAh) / Average Current Draw (mA). For example, a 3000 mAh battery powering a device that draws 200 mA will last approximately 15 hours (3000 / 200 = 15). However, this is a theoretical maximum. Real-world battery life is typically 80-90% of this value due to internal resistance, voltage regulation inefficiencies, and the fact that batteries cannot be fully discharged to zero without damage. Battery Life Calculator accounts for these factors through the efficiency percentage input.

What is battery capacity and what does mAh mean?

Battery capacity measured in milliamp-hours (mAh) represents the total amount of electrical charge a battery can store and deliver. One mAh means the battery can supply 1 milliamp of current for 1 hour, or equivalently 2 milliamps for 30 minutes. Common battery capacities include 2000-5000 mAh for smartphones, 3000-8000 mAh for tablets, 40000-100000 mAh for laptops (expressed as 40-100 Wh), and 100-500 mAh for IoT sensors. The capacity rating is measured at a specific discharge rate, and actual usable capacity can vary depending on how fast you draw current. Higher discharge rates typically yield slightly lower effective capacity due to internal resistance losses and heat generation.

What is duty cycle and how does it affect battery life?

Duty cycle is the percentage of time a device is in its active or high-power state versus its sleep or low-power state. A 50% duty cycle means the device is active half the time and sleeping the other half. This dramatically affects battery life because sleep mode typically consumes 10-100 times less current than active mode. For example, a sensor that draws 100 mA when active and 5 mA when sleeping with a 10% duty cycle has an effective average current of (100 x 0.10) + (5 x 0.90) = 14.5 mA, extending battery life nearly 7 times compared to always-on operation. Optimizing duty cycle is the single most effective strategy for extending battery life in IoT and embedded devices.

Why does battery efficiency matter for battery life calculations?

Battery efficiency accounts for energy losses that prevent you from using 100% of the rated capacity. These losses come from several sources. Internal resistance converts some energy to heat during discharge, typically wasting 5-15% of capacity. Voltage regulation circuits in your device waste additional energy converting the battery voltage to the levels needed by various components. Self-discharge causes batteries to lose charge even when not in use, at rates of 1-5% per month for lithium batteries. Temperature effects can reduce effective capacity by 10-30% in cold conditions. Finally, most devices shut down before the battery is fully depleted to prevent damage. A realistic efficiency value is 80-90% for lithium-ion batteries in normal conditions.

What factors reduce real-world battery life below calculated estimates?

Several factors cause real-world battery life to fall short of calculated estimates. Temperature is a major factor, with lithium batteries losing 10-20% capacity at freezing temperatures and degrading faster in high heat above 40 degrees Celsius. Battery aging reduces capacity by approximately 20% after 500 charge cycles. Peak current demands during processor-intensive tasks or radio transmissions cause voltage drops that waste energy through internal resistance. Background processes and wake events increase average current above expected levels. Power management circuitry such as voltage regulators typically operates at 85-95% efficiency. Parasitic drain from protection circuits and voltage monitoring adds a few microamps of constant draw. Account for these factors by using a conservative efficiency value of 70-80% for realistic estimates.

How do different battery types compare for device applications?

Different battery chemistries offer distinct advantages for various applications. Lithium-ion (Li-ion) batteries at 3.7V nominal offer high energy density of 150-250 Wh/kg and 500-1000 charge cycles, making them ideal for phones and laptops. Lithium polymer (LiPo) batteries have similar chemistry but can be manufactured in thin, flexible shapes. Lithium iron phosphate (LiFePO4) batteries offer 2000+ cycles but lower energy density, good for solar applications. Alkaline AA batteries provide 1.5V with 2500-3000 mAh capacity for low-drain consumer devices. Lithium primary cells like CR2032 coin cells offer 230 mAh at 3V with 10-year shelf life for IoT sensors and wearables. Nickel-metal hydride (NiMH) rechargeable AAs provide 1.2V with 2000-2800 mAh for moderate drain applications.

References

Reviewed by Daniel Agrici, Founder & Lead Developer ยท Editorial policy