(inspired by @subjectivist's and @caius-jard's answers)
increase your supply of rechargable batteries and rotate their usage.
e.g. with four batteries you can charge all 4 → use 3 → when they're done, you're left with 1 charged and 3 uncharged → charge 2 → 3 charged ready for use + 1 uncharged waiting for the next chance to charge → when the batteries are ...
Cell phone batteries (and everything else nowadays) uses Lithium Ion batteries. Unlike previous generations, these don't have a "memory" effect, so there's no need to completely discharge them all the way and then recharge them. In fact, frequently adding small amounts of charge (like taking it on and off a wireless charger) is a recommended use case.
The safe bet, although a bit more expensive, is to use 6 batteries:
use 3, recharge 2, 1 left empty;
use the other 3, recharge 2, 1 left empty;
recharge the 1+1 left empty batteries.
This will ensure uniform proper charging / discharging cycles for all batteries.
There might me a slight concern that some batteries will stay dis-charged for some time, ...
The other answers concentrate on what to do with an idle phone. However, you must understand which are the biggest energy eaters:
the main processor;
the video processor.
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 ...
First of all, do NOT just short circuit the battery charger with a piece of foil to force it to charge your battery individually. Looking at the spec sheet provided, your charger outputs 3V to each pair of batteries to charge them in series. If you place a single battery in the charger and force it to charge, then your charger will be supplying 3V to a 1.5V ...
These batteries are so inexpensive, I suggest you just purchase the correct one. Then you have no worries about damage or continuity of contact or anything else. I know what it is like to have little money but you can buy the right battery for $1 or even less if you shop around.