Battery Life Calculator - Runtime Estimator
Free Battery Life Calculator estimates runtime from battery capacity, current draw, and discharge safety. Works for phones, laptops, and electronics.
About This Calculator
The Battery Life Calculator - Runtime Estimator helps you estimate how long a battery will last based on its capacity and your device's power consumption. It is designed for anyone using phones, laptops, cameras, drones, IoT devices, UPS systems, or DIY electronics projects. Enter your battery capacity in mAh, the device's current draw in mA, and an optional discharge safety percentage to get a realistic runtime estimate.
The calculation uses the standard battery life formula: Battery Life (hours) = Battery Capacity (mAh) / Device Current Draw (mA) × (1 - Discharge Safety / 100). The formula accounts for discharge safety to prevent deep discharge damage in sensitive batteries like LiPo. For most consumer devices, a discharge safety of 0% is appropriate, while drone and hobby batteries often use 20% safety to extend battery lifespan.
Frequently Asked Questions
How do you calculate battery life?
Battery life in hours = Battery capacity in mAh divided by current draw in mA. A 3000mAh battery powering a 500mA device lasts 6 hours. Actual results vary due to discharge safety, temperature, and device efficiency.
Why does actual battery life differ?
Actual life is 70-90% of calculated due to self-discharge, temperature, battery age, conversion efficiency, and varying power draw from background apps and screen brightness.
How to extend battery life on devices?
Reduce screen brightness, disable background apps, turn off Bluetooth and WiFi, use power-saving mode, and avoid extreme temperatures for longer battery life.
What is a good battery life for a phone?
A good smartphone provides 3000-5000mAh, offering 8-14 hours screen-on time or 24-48 hours mixed usage. Look for 4500mAh+ for power users.
How do I measure battery capacity?
Battery capacity is measured in mAh. Use a USB power meter for accuracy. Smartphone apps like AccuBattery estimate capacity by measuring charge current and time.
Does fast charging reduce battery life?
Fast charging generates heat, accelerating degradation and reducing lifespan by 10-20% over 2-3 years. Use standard charging overnight for maximum battery health.
How to check battery health on devices?
On iPhones go to Settings > Battery > Battery Health. Android users can dial 4636 or use AccuBattery. Laptop users can run powercfg /batteryreport on Windows.
What is discharge safety and how does it affect runtime?
Discharge safety is the percentage of battery capacity reserved to prevent deep discharge damage. Common values are 20% for LiPo batteries and 0% for devices with built-in protection. Higher safety reduces usable runtime but extends battery lifespan.