[rwestergren]

I shared this elsewhere but I could have expressed the initial problem a little clearer, which actually was "enter my home without unlocking my phone which causes my phone to die in the cold."

Unlocking the screen caused the battery to drop immediately - it still had network connectivity prior to that.

[ivanbakel]

I think the initial problem was clearly-enough stated, and the GP's point is valid - why bother accounting for the case where your phone is so close to dying that you can't unlock the screen, when just a bit less battery life would mean that your phone dies regardless (and you're stuck outside anyways)?

[rwestergren]

The battery level isn't actually close to dying, in my case it just rapidly depletes from up to 40% when it's very cold. But that 40% remains intact seemingly with the screen off. Could be my phone also, but it has happened often enough that I wanted to solve it and thought this was an interesting approach.

For me, this was just a matter of convenience and not optimizing for most resilient or reliable solution. I do have backup plans for home entry.

[Majromax]

Batteries are generally less able to source current when very cold. At low temperatures, the battery was sufficient to power your phone in a low-draw state (minimal network activity, no screen, low power CPU state), but the voltage dropped when current draw increased.

[markstos]

I experienced this. I ran to work at -10F. When I arrived, I took out my phone to take a photo of my ice beard and although it almost immediately died.

[bmilleare]

I had no idea this was a thing. How cold are we talking for this to be something that happens often?