FAQ - Frequently Asked Questions - Designing IoT devices for long battery life
Intro
Battery lifetime in an IoT device depends on the complete system: wireless technology, transmission interval, sensor duty cycle, firmware behaviour, regulator efficiency, sleep current, battery chemistry and operating temperature.
A low-power wireless module alone does not guarantee long battery life. The full energy profile must be calculated and tested under realistic conditions.
Key technical selection criteria
Evaluate:
- target battery lifetime
- battery type and capacity
- sleep current
- active current
- transmission current
- transmission interval
- sensor measurement time
- microcontroller wake-up time
- regulator quiescent current
- network registration time
- operating temperature
- battery self-discharge
- peak current capability
Energy budget approach
Calculate the energy per operating cycle:
Total energy = sleep energy + measurement energy + processing energy + transmission energy
Then compare this with usable battery capacity, not only nominal capacity.
A device that sends data every minute has a completely different profile from a device that sends data once per day.
Wireless impact on battery life
Wireless communication is often the largest energy consumer in an IoT device.
Check:
- message size
- signal quality
- retry behaviour
- network registration time
- transmit power
- connection interval
- firmware update requirements
Poor signal quality can strongly reduce battery life because the radio may transmit longer, retry more often or use higher output power.
Power supply considerations
The power architecture must support both low sleep current and high peak current.
Review:
- regulator efficiency at light load
- regulator quiescent current
- voltage drop during transmission
- battery internal resistance
- capacitor placement
- low-temperature battery behaviour
- leakage paths on the PCB
Common mistakes
- calculating only average current
- ignoring sleep current
- ignoring regulator quiescent current
- underestimating wireless peak current
- testing only at room temperature
- using too frequent measurement intervals
- choosing the battery too late
- forgetting battery self-discharge
- not testing under poor signal conditions
Decision checklist
Before finalising the design, define:
- how often the device wakes up
- how long each measurement takes
- how much data is sent
- which radio technology is used
- expected signal quality
- required battery lifetime
- operating temperature range
- usable battery capacity
- peak current requirement
- firmware update strategy
CTA
Need help selecting low-power components, wireless modules or power management solutions for your IoT device? Contact the TOP-electronics technical support team.
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