We all use phones. Sometimes our phone's battery gets low and we have no resources to charge it.
What is the best solution for preventing our mobile phone from turning off, while it is in battery saver mode?
This link might be helpful to you.
In general, killing extra background processes and possibly switching off Bluetooth, Mobile Data and even WiFi for short durations of time will help extend the life of your smartphone. Putting your phone on airplane mode is also an effective strategy but you obviously won't be able to receive calls then.
Modern batteries are practically not affected by memory problems: as a consequence their life can literally be measured by a composition of switch on time, operating temperature, total current drained.
This means that you need to minimize all those factors: reduce the current needs (for instance by switching off unused applications or background tasks), reduce temperature (avoiding heavy enclosures or similar things), switch off the phone when not needed (f.i. during the night).
Lithium-ion batteries ability to hold charge decreases over time, and some factors may hasten that demise. Two main factors which will accelerate degradation of batteries are:
In order to minimise DoD losses, when possible charge battery before it drops down to zero.
As for temperature degradation, charge/operate the phone away from sources of heat such as laptop fan outlet/TV/radiator/other chargers.
Other tips which others did not mention that may help you with (slight) energy conservation.
Constant colour icon theme.
If using Android device you can achieve above quite easily with Tasker, it can automatically turn on your additional custom tweaks when standard powersaving mode is enabled.
The other answers concentrate on what to do with an idle phone. However, you must understand which are the biggest energy eaters:
What does it mean? If you keep the screen on for a long time, the battery will drain fast, even if you only browse the internet. In this case, the "hack" is to lower the screen luminosity to the minimum, while still being able to use the phone. Other hacks apply also.
About the two processors: they are used most for two types of activities:
Please note that for these activities, the screen is going to be turned on as well, so you are in the worst case of worst cases.
Bottom line: If you are (e.g.) traveling and you know you will not be able to recahrge the phone, refrain yourself from using the phone altogether, except for when really needed. Do not browse, do not chat, do not watch videos, do not play games.
All other advice and hacks apply.