We recently deployed 6 hydromoths at nearshore coral reef sites in Indonesia. All units were programmed to record with a sleep/record cycle of 50s recording and 10s sleep. After 3 days, we checked the units underwater and noticed that the units were not recording correctly. The red and green LEDs were flashing together. Their flashes matched this error: "Short flashes (10ms) of both LEDs between recordings mean an earlier scheduled recording has been cut short due to a recording failure." We noticed that after ~two days of successful recording, the recorders began saving shorter and shorter files, until they stopped saving files entirely. This happened on all six units.
Reading posts in this forum, it seemed that bad batteries was the most likely culprit. So, we did some tests using different battery types, including some that were recommended by colleagues who do PAM in the region. I have attached the results of this test here. We originally deployed with ABC batteries, and it is easy to see why there was an error after two days. In our test, these batteries started out with a combined voltage of ~3.7 V. But for the other two battery types, AA Alkaline Krisbow and AA Alkaline Energizer Max Plus, the voltage starts out at 4.9 and then drops to < 3.6 V in just two days. The hydromoths were updated to the latest firmware for this test.
Why are these batteries draining much faster than expected? What advice do you have for our team so that we can attain the expected recording duration (~7 days) for these hydromoth units using alkaline batteries. We still would like to record continuously and keep this sample rate.
Our team from Indonesia to Ithaca sincerely appreciates your help! Thank you.
Hi Alex, Just wanted to follow up. We did a test with a new SD card (Sandisk Extreme Pro 256 GB) and it fixed the issue. The unit recorded as programmed until the end of Day 7 when the batteries ran out of juice (we were using a set of gently used batteries for this test). Many thanks for your help.