These safety devices are not unique to winter camping, and plenty has been written on these in other media. We thought we would mention them here relative to battery performance.
The Personal Locator Beacon (PLB) has a special lithium battery, and on my unit it is rated to -40. PLB’s are for life and death situations only, since they trigger an airborne rescue launch where SARTECH’s may parachute out of aircraft to get to you, risking their own lives. A rescue costs 10’s of thousands of dollars and you may be charged for the full cost of a false alarm. I have never heard of a PLB battery malfunctioning in the cold, but I am not aware of any data of them actually being triggered at that temperature. It would be a very rare occurrence if there is data. Once triggered, there is a red light which shows it is on. If the light does not come on, then you could attempt to warm the unit on your body for several hours if your battery is weak. This is obviously problematic to do this, as it is already a life or death situation. It could perhaps be more effectively warmed with a very hot water bottle and wrapped in insulation. Holding it close to a fire risks melting the plastic, and lithium batteries must not be heated to dangerous levels.
The SAT (satellite) phone is a 2-way communications device with special lithium batteries that are sensitive to deep cold. I have used mine at about -10 with no problem. However as batteries age their ability to hold a charge is less, and cold will diminish the performance of these batteries. I have heard several stories where fully charged SAT phone batteries were dead in the cold. The only way to warm these batteries is on your person or with a hot water bottle. Holding it close to a fire may be dangerous, and it would warp the plastic so that the electrical contacts may no longer connect to conduct power.
Because SAT phone batteries can easily fail in the cold, and there have been connection problems with satellites of one company in particular, I recommend not scheduling regular call-ins. You cannot count on regular battery performance unless you are pre-warming the unit, so if a call in schedule is arranged and your home contacts don’t receive a call because your phone’s batteries are dead, then folks may trigger a needless rescue, which will not go down well with rescue authorities. You may get charged for wasted rescue expenses.
Cell phones are not covered here. Way out in the back country, there may be no coverage.