Prolong life of Mobile Phone Battery
Mobile phones are frustrating because their batteries don't last long, 1 year is about it, but this article from several years ago may help you get more life out of yours. Basically try not to let phone's battery fully discharge very often, ideal to start recharge at about 50% (Depth of Discharge below 90% greatly decreases total number of hours you can get from it so if you do the math a DoD of 50% is about ideal), Try not to allow phone to get much hotter than your body's temperature. I.e. not in full sun on dashboard or leave it in car (I do this often when I go kayaking, but better to put in dry box/bag and take with me). Don't overcharge it and leave it on a charger that does not stop charging automatically when fully charged. The newest Samsung S6 and similar phones can be recharged with a Qi inductive pad (no cord to phone), hopefully the soon to be released iPhone 7 will also have this feature and save a lot of $ on those irritating cables. A good quality Samsung Qi pad is about $13 on eBay, about the price of an iPhone cable (BTW Apple should replace this during the first year). Replacing the batteries on either an S6 or any of the iPhones yourself is almost like brain surgery or old fashion watch repair, NOT user serviceable! If cat jumps on table during this operation tiny screws not on tape or in containers are lost forever! Cat is shot kids cry...LOL not really.
http://batteryuniversity.com/learn/a...ased_batteries
So unless you have a "janky" service provider like mine, Sprint, with no cell towers unless you are near a major Intestate, you may consider your mobile phone an emergency survival tool to call for help in true survival situations if you can climb to a high point and get a signal. So a battery that last a long time even a year or more after purchase is a good thing. Resorting to eating that cat jerky is not! I'm only joking about the cat, no flaming please I take good care of my kid's cats because my kids just ignore them most of the time and I cannot allow an animal to suffer.
What works for me, not perfect
No technology is perfect, best to find something that works best for your lifestyle and learn how to maintain it as best you can. That is what I have learned after a few decades as an Electronic Design Engineer, nothing I ever designed was perfect and that never kept me up at night, compromises are necessary. I agree with Rick a good strategy is to have one or more backup batteries. Also according to this "Battery University" keeping Li-ion almost always above 90% charge is better than deep cycling (allowing to go dead) so Rick's plan may help his battery last longer as well, better if charger auto-shuts off when it reaches full charge.
With my old Samsung S4 I had two extra 2600 mAh batteries that I could easily replace by popping off the back. These are very small and light, take little space even when ultra light backpacking and can get me by for a week or more no problem. But I also have an external Li-ion USB battery that is more than 10 times that capacity and a bit bigger than the phone. So if phone is my only camera it sort of worked.
Finally after much delay (can get new phone every 18 months or less) I upgraded to Samsung Galaxy S6 since I have been with Sprint for many years they only charge me an extra $5/month for the lease, but a friend has been with them longer and gets his for $0/month. As I said earlier it is much more difficult to swap batteries, best just to use external, also the entire backside of S6 is glass so best to use a protective case which adds weight and bulk. But the new micro Processor is efficient so if GPS and Wi-Fi etc. is turned off it lasts about 2 days, but better to recharge before it gets much below 50% battery capacity to not stress out Li-ion. Better to stress out external battery instead which is a cheap eBay replacement. BTW Qi inductive charger is only about 0.5 amp charge rate so may not keep up with GPS when in car navigating, need USB plugged into phone with 1-2 amps for that. Phone is almost useless as a trail GPS, need a different Garmin or some other device for that.
A friend who flies RC airplanes both gas and electric told me that Li-ion batteries work best when hot. It may be true that they output the most amperes when hot but this does not prolong their life so at least for your phone, tablets and laptop computers I would advise against allowing our devices to get any hotter than they need to be, like in your pocket. NOT in full sun of a car’s dash board or car seat! Camping in the summer or just day hiking and paddling etc. some heat even well over 100F is just unavoidable. This may be why I go thru a lot of batteries.
I checked into T-Mobile/ Trac Phone for minimal service for a flip-phone it is only about $7-10 per month Extra $45 or less for kit to add to existing phone if you don’t like theirs and can root yours, but IMO a better backup communication for about $15+/month is something like SPOT Messenger, ACR PLB, Delorme etc. with 2 way txt msg via satellite if you go to very remote locations fairly often. Cheaper options if you just want someone to track your position back home on P.C. via satellite and GPS. Can even rent or share cost among outdoors friends. I just tell my wife: “When it’s my time, I’ll be off to see Jesus or oblivion whichever y’all catch up when you can… I love you, don’t worry about me.” Seriously I give her detailed trip plans and phone numbers.