I will complete the log later with the elements I was able to collect from the article on hackaday.com about the LoRaTube. There were a lot of comments about the long-term behavior of D cells. You’re right, I do have a modification to address this issue.

In the meantime, here is, through this diagram, the answer to one of the issues that was raised: there is indeed a clear separation between the electronics (which are in any case above the batteries) and the batteries, via the part that holds the 50 mm tube and looks like a coffee cup.