# Battery Life Calculator

Calculate how long a battery will last from its capacity (mAh), voltage, and device power draw. Includes efficiency adjustment for real-world estimates.

## What this calculates

How long will your battery last? Enter the battery capacity in mAh, voltage, and the average current draw of your device to get a realistic runtime estimate. The efficiency slider accounts for the fact that real batteries deliver less than their rated capacity.

## Inputs

- **Battery Capacity** (mAh) — min 1, max 100000 — Check your device specs or battery label
- **Battery Voltage** (V) — min 0.5, max 48 — Most phone/laptop batteries are 3.7V
- **Average Power Draw** (mA) — min 1, max 50000 — Average current consumption during use
- **Efficiency Factor** (%) — min 50, max 100 — Real-world batteries deliver ~80-90% of rated capacity

## Outputs

- **Estimated Runtime** — formatted as text
- **Runtime (hours)**
- **Battery Energy**
- **Power Consumption**

## Details

The basic formula is:

Runtime (hours) = Battery Capacity (mAh) x Efficiency / Current Draw (mA)

Common battery capacities:

  - Smartphone: 3,000-5,000 mAh

  - Tablet: 5,000-10,000 mAh

  - Laptop: 40-100 Wh (10,000-27,000 mAh at 3.7V)

  - Power bank: 5,000-20,000 mAh

  - AA battery: ~2,500 mAh (1.5V)

Real-world efficiency is typically 80-90% due to heat, voltage regulation, and battery degradation over time. Older batteries may drop to 60-70% of original capacity.

## Frequently Asked Questions

**Q: What does mAh mean?**

A: mAh stands for milliamp-hours. It measures how much charge a battery can store. A 5,000 mAh battery can deliver 5,000 mA for 1 hour, 2,500 mA for 2 hours, or 500 mA for 10 hours. Higher mAh means longer battery life at the same power draw.

**Q: Why does my battery not last as long as calculated?**

A: Several factors reduce real-world battery life: battery degradation over time, temperature effects (cold reduces capacity), background apps and processes, screen brightness, wireless radios (Wi-Fi, cellular, Bluetooth), and varying power draw during different activities.

**Q: What is the difference between mAh and Wh?**

A: mAh measures charge capacity, while Wh (watt-hours) measures energy capacity. Wh = mAh x Voltage / 1000. Wh is more accurate for comparing batteries at different voltages. A 5,000 mAh at 3.7V = 18.5 Wh.

**Q: How can I extend my device's battery life?**

A: Reduce screen brightness, disable unused wireless radios (Bluetooth, GPS), close background apps, enable power-saving mode, avoid extreme temperatures, and keep your battery between 20-80% charge for longevity. Avoid full discharge cycles.

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Source: https://vastcalc.com/calculators/technology/battery-life
Category: Technology
Last updated: 2026-04-21