Choose Right Battery for your Beacon
---Magic of Beacon Battery Life
In enterprise Beacon deployment environment, in general, Beacon maintenance cost is higher than Beacon price. Right choice of battery type for your Beacon could save 2~ 6 times of the Beacon hardware maintenance cost. Beacon battery life is one major indicator of Beacon maintenance cost. All Beacon providers always claims their Beacon battery life is very long 2~5 years no matter what battery type it is. The article will give detail on how the battery life affect maintenance cost, how the battery life is calculated and the best practice to choose right Beacon for your user scenario.
Beacon maintenance cost
Let us image a deployment scenario for a medium size chain store. The chain store has 200 stores in the different cities. There are average 4 ~ 6 Beacons deploy in each store. Everyday there might be a few Beacons’ battery is running out. To replace them, follow 2 steps are needed.
Step#1 Identify the Beacons needs replacement: who and how to do the work? The article (http://blog.sensoro.com/ibeacon-battery-management-challenges-and-sensoro-solution/) gives more detail on the challenge.
Step#2: Take the Beacon from the mount, open it and replace battery: The Beacons might be mounted on the ceiling; stick under table with double side sticker. Professional worker might be needed for this work.
Overall, the Beacon maintenance work’s cost will be higher than the Beacon price itself. A beacon with longer battery life will decrease maintenance cost very much. For example, 3 years battery life’s maintenance cost will be less than 1/3 of the Beacon with 1 year life as at the first 1.5 years, the chance of battery running out is very low so that the inspection cost is low.
Magic of Beacon Battery Life
Almost all Beacon providers claims their Beacon have long battery life (2 ~ 5 years) not matter what battery is used. What’s the magic behind that? Actually, the Beacon battery life are majorly decided by following follow 3 factors:
Beacon configuration: The advertising interval and Tx power are 2 major configurations impact battery power consumption;
Chipset: There are several Beacon chipset providers in the market includes Ti, Nordic, Dialog etc.
Battery electric quantity: different battery type’s electric quantity varies much
Based on them, the battery life could be calculated and estimated. Let’s start on how the Beacon consumes battery power. Beacon is a Bluetooth device which are doing Bluetooth signal broadcast with special time interval. There are 2 kind power consumption:
“Static” power consumption: Even when the Beacon are not broadcast, it still consumes “static” power consumption. The “static” power consumption is even, i.e. different days consumption are identical;
“Broadcast” power consumption: When the Beacon are doing broadcast, it needs consume more power than “static” power consumption. The Tx power are the factor affect the power consumption. With same Tx power, each broadcast’s power consumption are identical. And more broadcast will consume more power. That’s why advertising interval affect power consumption. For example, if the advertising interval is 100 ms, there will be 10 broadcast/sec; if the interval is 200 ms, there will be 5 broadcasts/sec. And the “broadcast” power consumption rate of 100 ms interval is 2 times of 200 ms interval.
We could get following conclusion.
With same chipset, different Beacon providers’ power performance is identical.
The only way to compare the Beacon providers’ power performance is to compare their chipset.
Different battery supply has different electric quantity. The battery life calculation is simple, i.e.
Battery Life (day) = Electric Quantity / Power Consumption Per Day
More battery electric quantity does simply means longer battery life and they are linear relationship. The common used batteries and their electric quantity as below.
CR2032: ~ 250 mAh
CR2450: ~ 500 mAh
CR2477: ~ 1000 mAh
2 x AAA (3V): ~ 1300 mAh
2 x AA (3V): ~ 2200mAh (Alkaline) or 3000 mAh (Li)
4 x AA (3V): ~ 4400mAh (Alkaline) or 6000 mAh (Li)
We can see, with same chipset, 2 x AA powered Beacon have 2 ~ 3 times battery life of CR2477 powered Beacon.
Different chipset has different “static” power consumption rate and “broadcast” power consumption. As the Beacon’s PCA design is simple, different Beacon provider’s PCB design almost won’t impact the power consumption.
Nordic NFR51822:
Below is the data for Nordic chipset’s power consumption data (measure with Nordic company’s reference design).
Static consumption rate: 0.29 mAh / day
Broadcast consumption rate
Based on that, the battery life (days) for 1000 mAh battery is as below.
The advertising interval is critical configuration for the Beacon performance at enterprise environment. In general, less interval leads to higher performance. It will affect following user experience.
Signal stableness: With less interval, Smart Phone could detect more stable signal RSSI. The stableness is critical for indoor positioning. So for the indoor positioning, the recommend interval is 100 ms;
Detecting rate: There is chance Smart Phone misses Beacon signal even in range. With less interval, Smart Phone has more chance to detect Beacon. For the notification pushing scenario, the recommend interval is 300 ~ 400 ms;
Connection rate: Smart Phone APP needs to connect to the Beacon to collect information such as battery level or change configuration such as UUID/Major/Minor. Less interval will lead to higher connection succeed rate. When the interval is less than 1200 ms, it is very hard to connect to the Beacon even the Smart Phone and the Beacon is back to back.
With the CR2477 (1000 mAh), some Beacon provider (Nordic chipset) claims that it has 5 years battery life. That means it is estimated with 2000+ ms interval. This configuration DOESN’T work in any user scenario.
Ti CC2541:
The Ti chipset’s data is as below.
Static consumption rate: 0.048 mAh / day
Broadcast consumption rate:
Based on that, the battery life (days) for 1000 mAh battery is as below.
Based on that, there is following conclusion,
The Nordic chipset Beacon is 1.5 times to 2.5 times of Ti chipset Beacon.
The advertising interval has much more impact than Tx power on battery life. Note: Some Beacon provider introduces battery life based on Tx power. It is a trick as it could make the battery life much longer.
Best Practice for Battery choosing
In general, larger electronic quantity battery means longer battery life. Longer battery life will decrease maintenance cost. But the larger electronic quantity battery is no free, in general, it might leads to larger size and higher cost.
There are some factors needs trade off.
Size: There are more and more requirement to “hide” Beacon in live deployment. Large size Beacon means hard to “hide”. Coin battery is smaller than AAA, AA battery.
Environment: Alkaline battery and Li battery are most common used battery. Alkaline’s electronic quantity varies much with environment temperature. In general, higher temperature leads to higher electronic quantity. But temperature has much less impact on Li battery. So if the Beacon will be deployed in outdoor with very cool environment, Li battery is better than Alkaline.
Battery type: With same size, Li battery electronic quantity is higher than Alkaline battery.
Cost: Li battery costs more than Alkaline battery but it has higher performance; Coin battery price is higher than AA and AAA battery but it is smaller.
Recommendation
Choose Chipset with less power consumption;
With consideration of size limitation, “larger” battery supply is better;
No one type power supply suitable for any scenarios. Multiple type battery types are needed for enterprise deployment, for example, USB Beacon is best for location wall plug; choose other battery supply beacon based on size limitation.
