There are two affects at work here.

1. A battery's self-discharge rate is lower at cooler temperatures. Storing a device in cool temperatures slows the loss of power over a battery's life.

2. The amount of energy that can be extracted from a battery goes up with higher (reasonable) temperatures. In other words, the amp-hours may be there, but the device may not be able to use them until the battery is warmed up.

The PLB can't be inside a parka or clothing when running. But if there is a motor running or some other source of heat perhaps the PLB can be atop it for warmth once activated.

I am puzzled as to what sort of batteries PLBs use. The operating temperature range and 5 year shelf life imply Lithium ... but I'd expect a 10-20 year shelf life in that case.

And the run time seems short ... if caught in a blizzard I'd be tempted to wait to hit the button until I thought SARS could get out so my beacon would still be running as they tried to close in on me.