This is what I recently created to enclose newbie PCB with two AA batteries.
https://www.thingiverse.com/thing:3228067

@mfalkvidd that's helped me a lot to better understand what is happening during send! Thanks!

I'm still investigating my problem :)

I checked logs from gateway and I can't see received messages with battery level, so looks like message is not reaching a gateway at all.

Situation improved a bit when I started using sendBatteryLevel with ACK, but it is still not perfect :).

I suspect that because sendBatteryLevel is a first message send after arduino wakes up maybe it could be that transport layer is not initilized yet? Maybe I should wait few sec after wake up before I start sending messages? What do you think?