To overcome the reduced battery power in cold temperatures, I bought some 3mm thick adhesive neoprene foam mat. I wrapped one of my batteries in it, and took Phoebe out to fly. She behaved beautifully over several flights so I’ve popped the latest code up to GitHub. Note there are no significant changes here, just temperature diagnostics and some tidying.
The battery is now held down by just a single silicone rubber band. The tension in the band compresses the foam cover a little which keeps the battery locked in place, and the neoprene protects the battery from the frame on the underside – a couple of unexpected benefits.