Abnormal battery voltage reading during USB recharge (my second Airnote device)

After some days of cloudy weather, the LiPo cell voltage of my second Airnote (a replacement) dropped for the first time down to 3.5 V and the device stopped transmitting data. Hence I connected the Airnote’s USB port to a Samsung cell phone wall-plug charger, an EP-TA20EWE .

The day after, Grafana’s dashboard showed that the voltage had increased up to the abnormally high value of 4.9 V, the same problem I wrote about in a previous post dealing with my original device (see “Issues with USB charging of Airnote’s battery”, September 21st, 2021). I removed the USB supply and the monitored voltage settled down to 4.19 V, a normal value for a 3.7 V fully loaded cell. Please refer to the attached screen capture.

These questions arise:

a) Are the dangerously high values of the battery voltage during the charge periods just an artifact of the monitoring circuit?
b) How reliable are Grafana’s voltage readings?
c) Is it safe to keep the 5 V USB supply continuously connected to the Airnote?

Thank you very much and best regards,


Hi @AlberTO,

Good question and thanks for the detailed description. The primary issue here is with labelling: the “battery voltage” should just read “voltage” in the UI as this is the voltage being supplied to power the Airnote (i.e. the max of the battery voltage and USB voltage when plugged in).

Yes it’s safe to leave the Airnote plugged in permanently. And actually the Airnote will increase the frequency of its measurements when power is supplied via USB.


Thank you very much, Rob, now it’s clear!

I warmly recommend to modify the label of the dashboard panel. Something like, for instance, “Device Supply Voltage”. This info should be included also in the user manual.

Best regards,