Right, so I’ve made some progress! Dug one of the Nests out of the basement and confirmed that it has a USB socket which, I think, might able to power it. It had enough juice left in it that I actually managed to pair it with Homey but then it promptly died before I could play around in VThermo.
The only difficulty I forsee (and it’s fairly major) is that the Nest is in two pieces - the front which has the screen and sensors and a back plate which contains the connection sockets for where you plug in the wiring if you were to connect it to a HVAC system. When the two parts are connected the USB port is inaccessible… And it’s yet unclear if they need to remain connected for the thermostat to function just enough to work with VThermo.
Will need to wait for the built-in battery to charge up a bit to see… But I’m not optimistic haha