Battery Life Calculator - Calculate Device Runtime
Free battery life calculator to estimate accurate runtime from battery capacity, voltage, load power, efficiency, and real-world usage.
Battery Life Calculator
Results
Estimates assume stable load and linear discharge. For safety-critical systems, design with extra margin and validate against real measurements.
What is a Battery Life Calculator?
A battery life calculator is a technical planning tool that converts your battery capacity, voltage, and device power consumption into a realistic runtime estimate. Instead of guessing, it uses watt-hour based formulas that apply efficiency, safety margin, and active versus standby usage.
This calculator works for:
- Smartphones, tablets, and laptops — Screen-on, mixed use, and standby runtime planning.
- Cameras, drones, and creators — Shoot or flight time per pack for field work.
- IoT, routers, and backup systems — Sizing power banks, UPS, and solar setups.
To understand how long file transfers or updates will run on your battery-powered devices, check out our Download Time Calculator to compare runtime against real data transfer durations.
For sizing networked equipment and always-on gear sharing the same power source, explore our Bandwidth Calculator to model data loads that indirectly influence power usage.
To verify if your server or NAS battery backup is adequate, use our Server Power Calculator to determine continuous watt draw before feeding it into this runtime tool.
For precise display-related power expectations, try our Screen Resolution Calculator to understand how resolution and density choices impact device workloads.
To design full low-voltage systems that combine storage, network, and processing gear, use our Data Transfer Cost Calculator alongside this tool for both energy and bandwidth budgeting.
How the Battery Life Calculator Works
The core logic uses energy balance in watt-hours. All inputs are normalized to Wh for capacity and W for load, then adjusted for real-world efficiency and safety margin.
Where:
- mAh / Wh = battery capacity from spec sheet.
- V = nominal battery voltage.
- Pavg = weighted average power including active and standby states, multiplied by device count.
- Efficiency = DC-DC, inverter, and wiring losses.
- Margin = reserved percentage to avoid deep discharge.
Key Battery Concepts Explained
Capacity vs Power
Capacity (Wh) tells you stored energy. Power (W) is how fast you use it. Runtime is energy divided by power, adjusted for loss.
Average vs Peak Load
Short spikes do not define runtime. Use realistic average consumption over your real workload pattern.
Efficiency Losses
Regulators, converters, and inverters waste 5–20% as heat. We include an explicit efficiency factor.
Aging & Environment
Cold and aging reduce usable capacity; a margin keeps estimates honest for real deployments.
How to Use This Battery Life Calculator
Select Input Mode
Choose mAh/mA, Wh/W, or mAh + W based on your specs.
Enter Capacity & Voltage
Use rated nominal capacity and pack voltage.
Add Load & Devices
Enter average consumption and count of devices.
Set Efficiency
Leave 85–95% for DC, 80–90% for inverter-based loads.
Adjust Usage & Margin
Configure active time, standby draw, and safety headroom.
Review Runtime
Use hours and HH:MM outputs to validate your design.
Benefits of Using This Calculator
- • Engineering-grade logic: Uses Wh and W instead of simplistic mAh guesses.
- • Real-world aware: Includes efficiency, safety margin, and standby behavior.
- • Device agnostic: Works for phones, laptops, routers, cameras, drones, and IoT.
- • Quick comparison: Test multiple loads and capacities to right-size batteries.
Factors That Affect Your Battery Life
1. Load Variability
Heavy CPU, radio, and backlight usage increase power beyond nominal values; use realistic averages.
2. Temperature
Very low or high temperatures reduce effective capacity and usable voltage range.
3. Battery Health
Aged batteries store less energy; derate capacity for older packs or many cycles.
4. Conversion Path
USB power banks, boost converters, and inverters introduce 10–25% losses that must be included.
Frequently Asked Questions (FAQ)
Q: How do I get average power for my device?
A: Use manufacturer typical consumption, measure with a USB or DC power meter, or average readings from your OS battery statistics over normal usage.
Q: Why is my real battery life lower than theoretical?
A: Real usage includes peaks, radio activity, background apps, thermal limits, and aging. Our efficiency and margin inputs help align math with reality.
Q: Can this help size a UPS or power bank?
A: Yes. Enter total Wh of the battery or bank and combined watt draw for all devices to get runtime before shutdown.
Q: What safety margin should I use?
A: Use 10–20% for lithium-ion to avoid deep discharge and give conservative estimates, higher for critical systems.
Q: Does screen brightness really matter?
A: Yes. Displays are often one of the largest drains. Higher brightness and high-refresh panels significantly reduce runtime.
Q: Is this suitable for embedded and IoT design?
A: Absolutely. You can model duty cycles, sleep currents, and low loads accurately by adjusting active and standby inputs.