For those following this thread a quick update is that it is not working out and the Shelly Uni was apparently drawing more power than the solar panel/battery could provide. I tried flashing Tasmota onto the Uni with a 1hr update period, but that did not fare any better. Flashed ESPHome on there but forgot to add the OTA component so the Uni is in a sad state until the wired flash connector I ordered comes in. In the meantime I’ve replaced the Uni with a Wemos D1 mini with a mini buck converter.

I need a resistor before I can attach the pressure sensor so for now the D1 mini is just sitting in the enclosure chatting to Home Assistant once per hour sending the wifi signal strength and a couple other sensor values. I’ll update with findings. When I opened up the enclosure to add the D1 mini the battery was at about 12.6 which is just shy of max for lithium cells so this seems like a Uni problem.