FAQ: battery
It's reasonable to expect that ruuvi tags will continue to run for over 3 years at room temperature.
The RuuviTags ship with a 3 volt, 1000mAh CR2477 battery with an environmental operating range of -20 to +60°C. Batteries with extended environment ranges are available.
There is a very concerted effort that the distributed software use little power.
As of version 2.4.2
- RAWv1 consumes ~15 uA, and should last for 6 years
- RAWv2 consumes ~18 uA, and should last for 5 years
- RAWV2_slow consumes ~13 uA and should last for 7 years
There is significant reduction in life expectancy as temperature increases.
Predicting battery failure is extremely unreliable based on tracking battery voltage. This is largely due to the minor variation in output throughout most of the battery lifetime and the sudden degradation near end-of-life. Most Lithium / Manganese Dioxide (Li/MnO2, CR prefix) batteries start at just over 3.00V and drop to 3.00 within several hours after load is applied. They continue to output 3.00 volt slowly dropping to 2.7 for months (depending on temperature) with the distributed ruuvi software. At some point they drop rapidly below 2.00 volts.
High Res formats of packets include battery voltage and you should plan to replace the battery when the voltage drops below 2.5 volts
When the battery nears end-of-life momentary droops cause the processor to reboot. This is manifested in a resetting of the MeasurementSequenceNumber which normally resets at 65,534. (voltage shown times 100)
This tag mounted outside in Northern USA ran from 8/10/19 until 2/12/20 (voltage shown times 10)
Theoretical current usage for the nRF52832 radio itself is 5.3mA when transmitting at 0dBm, adding the peripherals needed to run the radio brings the requirement up to 7.1mA. Keeping the system idle most of the time significantly reduces the average current requirements.
Additional current is used by the environmental sensor(temperature, humidity and air pressure) and accelerometer.
Nordic has a Online Power Profiler which estimates the current consumed during data exchange. This can be used to demonstrate the effect of various configurations. For example at 4dBm with an interval of 100ms the total average current is 160uA. Reducing the interval to 1000ms reduces the average current to 10uA as you should expect.
The nRF52832 specifications recommend a 3.6 to 1.7 volt supply. (Although not used as of 2/27/19, nRF52832 provides brownout warnings at tenth volt variations from 2.8 to 1.7.)
A temperature/humidity/air-pressure sensor (BME280) requires a VDD main supply voltage range: 3.6 to 1.71 and VDDIO interface voltage range: 3.6 to 1.2.
Self-discharge is less than 1% per year at 23°C. Shelf life is up to 10 years at max. 23°C. The size of a CR2450 battery is 24mm diameter with a height of 5.0mm.
Of course not using a coin battery and using another 3 Volt battery or other source is always a possibility. Including pairing LiFeS2 AA 1.5V.
Informative graphs at Renata Design Guide
Effects of temperature Energizer lithium coin (be sure to scroll down to the correct type battery).
The battery shipped with the kickstart shipments was the 490mAh CR2450HT with an temperature operating range of -40 to +125 °C.
Extreme case battery only lasts 1 month! (voltage shown times 10)
