Eek, plan is not going as well as I hoped, turns out it’s an older version of the SG108 so it doesn’t run off 5V, it seems to half boot but isn’t enough. Looks like the modern versions of the device have some low power elements.
It’s not all bad, it’s meant to run off 9V and my solar system is 12V so I can step it down. The question is how efficient is it?