Enviro Grow wake reason problem

Hello, I’m still getting a wake reason: usb_powered even though I’m using the 3xAA battery pack and have nothing connected to the USB. Do you know what could be causing the problem? I’m kindly out of ideas! My enviro grow takes readings every 15 seconds no matter what setting I set… I tested with firmware 0.0.2, 0.0.8, 0.0.9…

My config :

# how often to wake up and take a reading (in minutes)
reading_frequency = 15
# where to upload to ("http", "mqtt", "adafruit_io", "influxdb")
destination = 'influxdb'
# how often to upload data (number of cached readings)
upload_frequency = 5

My log file:

2023-08-13 17:39:02 [info     / 134kB] > performing startup
2023-08-13 17:39:02 [debug    / 132kB]   - running Enviro 0.0.9, MicroPython 856e08b1931b88271816a2f60648f6ff332235b2, enviro v1.20.4 on 2023-08-04
2023-08-13 17:39:02 [info     / 125kB]   - wake reason: usb_powered
2023-08-13 17:39:02 [debug    / 124kB]   - turn on activity led
2023-08-13 17:39:02 [debug    / 119kB] > 88 blocks free out of 212
2023-08-13 17:39:02 [debug    / 116kB] > taking new reading
2023-08-13 17:39:02 [info     / 112kB]   - seconds since last reading: 14
2023-08-13 17:39:05 [info     / 127kB] > sensor A below moisture target 50 (currently at 0).
2023-08-13 17:39:06 [info     / 125kB]   - running pump A for 2.0 second(s)
2023-08-13 17:39:08 [debug    / 115kB] > caching reading for upload
2023-08-13 17:39:08 [info     / 110kB] > 1 cache file(s) need uploading
2023-08-13 17:39:08 [info     / 108kB] > connecting to wifi network 'XXX'
2023-08-13 17:39:13 [warning  / 129kB]   - took 5.298 seconds to connect to wifi
2023-08-13 17:39:13 [info     / 122kB] > uploading cached readings to Influxdb bucket: home
2023-08-13 17:39:14 [info     / 107kB]   - uploaded 2023-08-13T17_39_08Z.json
2023-08-13 17:39:14 [info     / 105kB] > going to sleep
2023-08-13 17:39:14 [debug    / 103kB]   - clearing and disabling previous alarm
2023-08-13 17:39:14 [info     / 100kB]   - setting alarm to wake at 17:40pm
2023-08-13 17:39:14 [info     /  98kB]   - shutting down
2023-08-13 17:39:17 [info     / 134kB] > performing startup
2023-08-13 17:39:17 [debug    / 132kB]   - running Enviro 0.0.9, MicroPython 856e08b1931b88271816a2f60648f6ff332235b2, enviro v1.20.4 on 2023-08-04
2023-08-13 17:39:17 [info     / 125kB]   - wake reason: usb_powered
2023-08-13 17:39:17 [debug    / 124kB]   - turn on activity led
2023-08-13 17:39:17 [debug    / 119kB] > 88 blocks free out of 212

Thanks in advance for your help!