Battery Life Calculator

Welcome to the Battery Life Calculator, a powerful tool for estimating how long a battery will power your device. Whether you are designing an IoT project, evaluating phone battery performance, planning for portable electronics, or sizing a power bank for your trip, this calculator provides accurate runtime estimates with detailed breakdowns.

How Battery Life Calculation Works

The fundamental formula for calculating battery runtime is straightforward:

For example, if you have a 3000mAh battery and your device draws 150mA of current, the theoretical runtime would be:

However, real-world battery performance is affected by several factors, which is why our calculator includes an efficiency adjustment.

Understanding Battery Capacity Units

mAh (Milliamp-hours)

The most common unit for small batteries. It measures how much current a battery can supply for one hour. A 3000mAh battery can theoretically deliver 3000mA for 1 hour, or 300mA for 10 hours.

Ah (Amp-hours)

Used for larger batteries like car batteries or large power banks. 1 Ah = 1000 mAh. A 100Ah car battery equals 100,000mAh.

Wh (Watt-hours)

Measures energy capacity rather than charge capacity. Often used for laptop batteries and power stations. To convert: Wh = mAh × V ÷ 1000. For a 3.7V lithium battery: 3000mAh × 3.7V ÷ 1000 = 11.1Wh.

Understanding Consumption Units

mA (Milliamps)

Current draw in milliamps. Most small electronics specify consumption this way. Smartphones typically draw 100-400mA depending on activity.

A (Amps)

Used for higher-power devices. 1A = 1000mA. A laptop might draw 2-4A at full load.

W (Watts)

Power consumption. Common for laptops and appliances. To convert to current: A = W ÷ V. A 45W laptop charger at 19V draws about 2.4A.

Why Efficiency Matters

Real batteries never deliver 100% of their rated capacity due to:

• Internal Resistance: Causes energy loss as heat during discharge
• Voltage Regulation: DC-DC converters in devices waste some energy
• Temperature Effects: Cold temperatures significantly reduce capacity
• Battery Age: Capacity degrades with charge cycles
• Discharge Rate: High current draw reduces effective capacity (Peukert's Law)

Typical efficiency ranges:

• 95-100%: New Li-ion battery, low discharge rate, room temperature
• 85-90%: Average conditions for most applications
• 75-80%: High discharge rate, older battery, or cold environment

Common Device Power Consumption

Tips for Maximizing Battery Life

For Mobile Devices

• Reduce screen brightness - screens consume 30-50% of battery
• Use dark mode on OLED screens - black pixels use no power
• Disable unused radios (WiFi, Bluetooth, GPS when not needed)
• Enable power saving modes for non-critical use
• Keep the battery between 20-80% for longevity

For DIY/IoT Projects

• Use sleep modes aggressively - wake only when needed
• Use a switching regulator for large voltage drops, or a low-Iq LDO when the drop is small
• Minimize wake-up frequency for sensor readings
• Use lower clock speeds when possible
• Consider solar charging for outdoor deployments

Frequently Asked Questions

How do I calculate battery life?

Battery life is calculated by dividing the battery capacity (in mAh) by the device consumption (in mA). The formula is: Runtime (hours) = Battery Capacity (mAh) ÷ Device Consumption (mA). For example, a 3000mAh battery powering a device that draws 150mA will last approximately 20 hours. Real-world results vary due to efficiency losses and varying power consumption.

How do I estimate battery life for a device that sleeps most of the time?

Work out the average current: (awake current × awake time + sleep current × sleep time) ÷ the length of one cycle, then divide the usable capacity by it. A sensor drawing 8 mA for 2 seconds every 10 minutes and 15 µA asleep averages about 42 µA, so a 225 mAh CR2032 lasts about six and a half months at 90% efficiency. Fill in the Sleep Mode fields and the calculator does this, adds self-discharge, and compares common batteries.

What is the difference between mAh and Wh?

mAh (milliamp-hours) measures electric charge capacity, while Wh (watt-hours) measures energy capacity. To convert between them, you need the voltage: Wh = mAh × V ÷ 1000. For example, a 3000mAh battery at 3.7V equals 11.1Wh. Wh is often used for larger batteries like laptops, while mAh is common for phones and small devices.

Why should I consider efficiency factor?

Battery efficiency accounts for real-world energy losses during discharge. Factors include internal resistance, heat generation, voltage regulation circuits, and battery age. A typical lithium-ion battery operates at 85-95% efficiency. Using an efficiency factor gives more realistic runtime estimates compared to the ideal calculation.

How do I find my device's power consumption?

Device power consumption varies by activity. Check your device specifications, use a USB power meter, or refer to typical values: smartphones typically use 100-400mA active and 5-15mA standby; laptops use 15-60W; LED flashlights use 100-1000mA; Arduino boards use 20-50mA. Gaming and high brightness significantly increase consumption.

Why does my actual battery life differ from the calculation?

Several factors cause real-world differences: varying power consumption during use (not constant), temperature effects, battery age and health, background processes, and the Peukert effect (high discharge rates reduce effective capacity). The calculation provides an estimate based on average consumption.

How long can a 10,000 mAh power bank run a 5 W device?

A rough estimate is about 6.3 hours if the bank’s 10,000 mAh rating is at 3.7 V and conversion efficiency is 85%. That is 37 Wh of stored energy, or about 31.5 Wh after the efficiency adjustment; dividing by a 5 W load gives 6.3 hours. Actual runtime varies with the bank’s usable capacity, output voltage conversion, and the device’s changing power draw.

Why can’t I compare two batteries by mAh alone?

mAh measures charge, not total energy, so the battery voltage matters. Convert capacity to watt-hours with Wh = mAh × volts ÷ 1,000. For example, 5,000 mAh at 3.7 V is 18.5 Wh, while 5,000 mAh at 12 V is 60 Wh. The higher-voltage battery stores more energy despite having the same mAh rating; account for conversion losses when estimating device runtime.

How do I estimate runtime for a sensor that sleeps most of the time?

Use the awake current, sleep current, awake duration, and wake interval to find the average draw. For example, a sensor drawing 20 mA for 1 second every 60 seconds and 0.1 mA while asleep averages about 0.43 mA. That comes from 20 × 1/60 plus 0.1 × 59/60. The calculator’s sleep inputs are intended for this kind of duty cycle; real runtime can still vary with battery losses and other activity.

Additional Resources

• Peukert's Law - Wikipedia