Battery life estimation for embedded and industrial devices
When a device runs from batteries, one of the most important questions is “How long will it last?” A battery life calculator turns capacity, load current and duty cycle into a practical runtime estimate so you can size the battery correctly and set realistic maintenance intervals.
Typical use cases include:
- Wireless sensors and data loggers
- Portable HMIs and handheld testers
- Back-up supplies for PLCs and controllers
- IoT nodes running from primary cells or small packs
Basic battery life equation
The simplest runtime estimate assumes a constant current draw and ideal battery behavior:
Battery life (hours) = Capacity (mAh) / Load current (mA)
For example, a 2000 mAh battery feeding a constant 100 mA load gives:
Battery life ≈ 2000 / 100 = 20 h
In real designs, however, current is often not constant. Devices sleep most of the time and wake briefly to measure, transmit or update the display. The calculator therefore lets you model active and sleep currents and combines them into an average current.
Average current with duty cycle
If a device alternates between active and sleep states:
- Iactive – current during active time
- Isleep – current during sleep
- D – duty cycle (fraction of time active, 0–1)
then the average current is:
Iavg = D × Iactive + (1 − D) × Isleep
Battery life becomes:
Battery life (hours) = Capacity (mAh) / Iavg (mA)
Peukert effect and derating
Real batteries do not deliver their full rated capacity at every load current. At higher discharge rates, the effective capacity drops; at very low rates, it may increase slightly. Temperature, age and cutoff voltage also influence usable capacity.
To account for these factors, many engineers apply a simple derating factor:
- Usable capacity = Nominal capacity × Derating factor
For example, with a 20% safety margin:
Usable capacity = 0.8 × Nominal capacity
The calculator can show both the ideal runtime and a derated runtime so you can plan maintenance or replacement intervals more conservatively.
Quick reference examples
The table below shows rough runtimes for a 2000 mAh battery at different average loads (ideal case, no derating):
| Average current (mA) | Estimated life (hours) | Estimated life (days) | Typical scenario |
|---|---|---|---|
| 10 mA | ≈ 200 h | ≈ 8.3 days | Small display, light sensors |
| 1 mA | ≈ 2000 h | ≈ 83 days | Low-power wireless node, frequent updates |
| 100 µA | ≈ 20,000 h | ≈ 2.3 years | Sensor with long sleep intervals |
| 10 µA | ≈ 200,000 h | ≈ 22.8 years* | Ultra-low sleep current (practically limited by battery self-discharge) |
*At very low currents, self-discharge and aging limit real lifetime long before the theoretical number is reached.
Using the Battery Life Calculator
- Enter battery parameters: Specify nominal capacity (mAh), number of cells if applicable, and an optional derating factor for real-world conditions.
- Describe the load: Enter either a single constant current or separate active and sleep currents with a duty cycle.
- Review average current and runtime: The tool calculates Iavg, ideal runtime and derated runtime in hours, days and (for low currents) years.
- Iterate on design choices: Adjust duty cycle, optimize sleep current, or choose a larger battery until the runtime meets your requirements.
Design tips for realistic battery life
- Measure real currents: Use a low-burden ammeter or power analyzer to capture actual active and sleep currents instead of relying only on datasheet values.
- Consider temperature: Capacity drops in cold environments and self-discharge increases at high temperature; both reduce real runtime.
- Account for cutoff voltage: Many devices shut down before the battery is completely empty. Use the capacity available between full charge and cutoff, not the theoretical value to 0 V.
- Plan for aging: Lithium and lead-acid batteries lose capacity over time and cycles. For long-life installations, design around end-of-life capacity, not fresh-cell capacity.
This battery life calculator gives you a quick, engineering-grade estimate of runtime for portable, backup and remote systems, helping you choose the right battery, optimize power consumption and reduce unplanned downtime in the field.
