I'm not a "prepper" -- I just want a way to get help for medical emergencies when there's a power outage mostly. I get where you're coming from, but a primary cell Lithium-Iron AA like an Energizer L91 (http://data.energizer.com/PDFs/l91.pdf) is up to 20 years -- probably more than the service life of the phone.

I have a phone like this from about 10 years ago that we leave at a family camp (super rough cabin with no utilities). With the loss of quality, power-outage survivable POTS phone service, this type type of device fills an important niche. 20 years ago, NYNEX (now Verizon) would provide dial tone for 10-14 days in the event of a blizzard or other power outage. Now you get 24-72 hours from cable/internet providers at best.

Another issue with conventional rechargeable batteries is they don't handle charging well when discharged completely. A cellphone left in a cabinet for 5 years is a brick in many cases.