# Cellular IoT – Part 10 – 10 Years Battery Lifetime

Another NB-IoT number floating around is that very power efficient NB-IoT devices should be capable to be driven from a small battery for more than 10 years without needing a recharge. Again, I wondered where this number comes from and which assumptions were made to declare that this is possible.

Again, the calculation can be found in 3GPP TR 45.820, for NB-IoT in Chapter 7.3.6.4 on ‘Energy consumption evaluation’.

The battery capacity used for the evaluation was 5 Wh. That’s about half or even only a third of the battery capacity that is in a smartphone today. So yes, that is quite a small battery indeed. The chapter also contains an assumption on how much power the device draws in different states. In the ‘idle’ state the device is in most often, power consumption is assumed to be 0.015 mW.

How long would the battery be able to power the device if it were always in the idle state? The calculation is easy and you end up with 38 years. That doesn’t include battery self-discharge and I wondered how much that would be over 10 years. According to the Varta handbook of primary lithium cells, self-discharge of a non-rechargable lithium battery is less than 1% per year. So subtract roughly 4 years from that number.

Obviously, the device is not always in idle and when transmitting the device is assumed to use 500 mW of power. Yes, with this power consumption, the battery would not last 34 years but less than 10 hours. But we are talking about NB-IoT so the device doesn’t transmit for most of the time. The study looked at different transmission patterns. If 200 bytes are sent once every 2 hours, the device would run on that 5 Wh battery for 1.7 years. If the device only transmits 50 bytes once a day the battery would last 18.1 years.

So yes, the 10 years are quite feasible for devices that collect very little data and only transmit them once or twice a day.

## 3 thoughts on “Cellular IoT – Part 10 – 10 Years Battery Lifetime”

1. Sebastian says:

I find it somehow interesting discussing battery lifetimes of >10 years.

Is it safe to assume that the backend / infrastructure the NB-IOT terminal sends its data to will actually persist for this time span?

Will somebody think it is necessary to do a software update to the NB-IOT Terminals after ~3 years? Or even 6 weeks after deployment because they realize they forgot something and did not cover it in the QA?

I’m really waiting for first experience reports in deploying NB-IOT services, such as parking spot sensors. We’ll be wiser soon(er or later…)

1. thomas giarimi says:

Well, GSM infrastructure is >15yrs and there are still no plans to dismantle. Ironically, taking down 3G/WCDMA will happen sooner.
So, 15 yrs old devices are still compatible.

And that, thank’s to the huge installed base of Machine-machine communication using GSM.

2. Wolfgang Busch says:

i have experience with low power gps/gsm tracking applications.
15years 1 cycle per day with 120 second gps signal search and 15 seconds “scan all gsm networks and transmit 120 bytes of data” is no problem with a D-size lithium battery.
really no marketing bullshit!
it uses goldcaps to use 100% of the battery power and after goldcaps charged by the battery for a few hours the whole circle is run by the power of the gold caps.
one of this devices is since 3 years on my desk and still shows 3,1V battery voltage (round about 80% full battery)

Wolf.