Hydromoth stops recording due to Recrding failure or low batteries

We are using hydromoths with Ni-MH 1.2 Volt and 2300 and 2500 mAh batteries and SanDisk ultra 64 GB SD cards.

These are the settings we are using:

Device ID : 242A26056486ACAC

Firmware : AudioMoth-Firmware-Basic (1.9.2)

Time zone : UTC

Sample rate (Hz) : 48000

Gain : Medium

Sleep duration (s) : 300

Recording duration (s) : 300

Active recording periods : 1

Recording period 1 : 00:05 - 00:00 (UTC)

First recording date : ----------

Last recording date : ----------

Filter : -

Trigger type : -

Threshold setting : -

Minimum trigger duration (s) : -

Enable LED : Yes

Enable low-voltage cut-off : Yes

Enable battery level indication : Yes (NiMH/LiPo voltage range)

Always require acoustic chime : No

Use daily folder for WAV files : No

Disable 48Hz DC blocking filter : No

Enable energy saver mode : No

Enable low gain range : No

Enable magnetic switch : Yes

Enable GPS time setting : No

Our problem is that the hydromoths will stop recording and show a flashing red and green LED indicating a low battery or SD card failure. After max 4 days the size of the audiofiles gradually decline. We have calculated that the audiomoths should record for at least a week. We suspect the problem might be the voltage level getting too low.

The file size keeps decreasing to 0 kBs and then the moths will stop recording.

Is this a reoccuring problem? Or could it be because of our batteries?