ARU Battery Longevity Report

This report summarizes efforts to determine the lifespan of batteries used in Song Meter Micro and AudioMoth ARU at various settings and conditions. Trials to compare changes in sample rate, gain, temperature, and battery type were conducted. Each category had three units at the same setting and were exposed to the same conditions. Every available sample rate and gain setting was tested as well as the effect that cold and freezing temperatures have on the ARUs.

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The report is licensed under CC-BY-4.0. Please feel free to use it with attribution.

Stahlman, Nickolus (2023). ARU Battery Longevity Report. GitHub repository: 
https://github.com/kitzeslab/ARU_battery_longevity. DOI:10.5281/zenodo.7640775

A summary of the report can be found below alongside tables that summarize the results of the sample rate and temperature trials. The full report can be accessed here

Summary

The longevity of batteries used in Song Meter Micro (SMM) and AudioMoth Autonomous Recording Units (ARUs) was evaluated at varying settings of sample rate, gain, temperature, and battery type. The control settings used for SMMs included a 32kHz sample rate with 18dB gain using Duracell Procell PC1500 AA batteries (Procell) to record at room temperature which recorded an average of 139 hours of audio. The lowest sample rate setting of 8kHz would increase the hours of audio by 61% and the highest sample rate setting of 96kHz would decrease the hours of audio by 34%. A sample rate of 96kHz caused the 64GB SD card to fill up before the batteries died; however, the batteries would die once the device was rebooted with a new SD card. The change of gain had a negligible effect on hours of audio recorded. Performance of the Procell batteries decreased by 10% at cold temperatures and by 43% at freezing temperatures. Energizer Ultimate Lithium AA (Lithium) batteries increased hours of audio recorded by 24% and performed at relatively consistent levels across room, cold, and freezing temperatures. Lithium batteries double the hours of audio recorded at freezing temperatures compared to Procell batteries at the same temperature. Panasonic Alkaline Power Plus AA (Panasonic) batteries were only tested at room temperature and resulted in a decrease of 10% in hours of audio.

The control settings used for the AudioMoths included a 32kHz sample rate with the medium gain setting using Procell batteries to record at room temperature which recorded an average of 189 hours of audio. The lowest sample rate setting of 8kHz would increase the hours of audio by 30% and the highest sample rate setting of 384kHz would decrease the hours of audio by 77%. Sample rates higher than 48kHz would result in the 64GB SD card to fill up before the batteries died. The change of gain had a negligible effect on hours of audio recorded. Performance of the Procell batteries decreased by 3% at cold temperatures and by 46% at freezing temperatures. Lithium batteries increased hours of audio recorded by 26% and performed at relatively consistent levels across room, cold, and freezing temperatures. Panasonic batteries were only tested at room temperature and resulted in a decrease of 7% in hours of audio.

A comparison of average hours of audio recorded at room temperature by SMMs and AudioMoths at every available sample rate setting using Procell batteries
Sample Rate (kHz)	Average Hours of Audio for SMM	Average Hours of Audio for AudioMoth
8	223	249
16	164	225
22.05	152	-
24	165	-
32	139	189
44.1	127	-
48	131	161
96	92	91
192	-	60
250	-	47
384	-	43

A comparison of average hours of audio recorded by SMMs and AudioMoths with a 32kHz sample rate at different temperature ranges using Procell or Lithium batteries
Temperature	Average Hours of Audio for SMM	Average Hours of Audio for AudioMoth	Average Hours of Audio for SMM	Average Hours of Audio for AudioMoth
	Procell Batteries		Lithium Batteries
Room (20.5°C)	139	189	167	234
Fridge (3.4°C)	125	183	174	241
Freezer (-16.1°C)	80	102	177	238