Aside from the heat problem I had more trouble with bike computers in Colorado commuting in the winter. Below 40 degrees they were unreliable. Below 30 degrees they went dead in minutes ifI had standard batteries. I do understand how cold slows the chemical reactions in the batteries. If it had mattered I could have gotten a voltage converter and run it off of my big, insulated headlamp battery.

If you hot riders can find no other way to keep your displays from going black get one of those electronic widgets that turns cold on one side when you put juice thru it and mount the computer on that side