question

It should already be doing this. It uses space on /data partition to store VRM data when off line if there is no external (USB or SD) storage. Usually there is plenty of space on internal storage. You can check in the VRM portal to see where the storage is and how much there is. It also shows how many records have been stored if the GX device is off-line.

Uploading the stored records to VRM does take a while. You might just need to be patient.

I experience this issue as well on data loggers we have built with Rapsberry Pi's. They do not log when the internet connection goes down.

I did a little testing this morning with my Raspberry Pi 3+ monitoring install. I am running v2.89.

I blocked the Pi's ability to connect out to the Internet, and connected to the VenusOS remote console on my local network. VenusOS did report that it could not contact VRM. I allowed the "Stored Records" count to climb to 20. Then rebooted. The records were retained after the reboot. I then unblocked the Pi to allow it to connect to the Internet. Within about a minute, all stored records had been uploaded to VRM.

Matt

There is another issue that many forget.

The pi has no real time clock, if you reboot the pi without internet connection it cannot get date and time from ntp, so the energy is logged at 1970. Once connection is established, this data will be uploaded and disappear in the past. You end up with a gap in your logging, because of the wrong time stamps.