Why don't cell phones use 5v batteries?
The other answers tell a good explanation for you on why we don't have 5v batteries so I won't be repeating what they have already said . I will though tell you that it isn't so much the voltage a battery can produce but the amperage it holds that makes a battery long lasting . There are step up and step down resistors and transformers in the circuits to regulate what voltage a component needs and they mostly need surprisingly little voltage in a smartphone . They do though require voltage to keep running and that is were the amperage capacity comes into play . When a battery can hold more amps it can provide a steady flow of electricity for longer periods of time . The problem though is the more amps you cram into a tight space the more potential you have for something to go wrong . With todays batteries storing thousands of milliamps of potential energy they can have devastating effects if they detonate , Note 7 showed this well with it's fire producing capabilities . Putting higher voltages would also increase the potential of even more destructive power without any real payoff accept being able to run through the power stored in a battery quicker than the 3.7v circuit .
they would never charge then.
In order to have a current ‘flow' you need to have a ‘potential difference'.
To accomplish this, and keep cell phones powered up, the phone uses a voltage that the cell can naturally produce.
So, the battery is designed to be less than 5V, and more than 3.
So, 3.7 was chosen, and the battery voltage can drop to 2.5 at its minimum.
It was chosen as more than three, so that it could not be replaced by two 1.5v cells spliced together. Why? we will never know.
Anyway, the value of 3.7 was discovered to work for the new cells , and they were what was designed for the the transistors of the new gadgets, and that is what was advanced into the cell phone.
So that is how it progressed.
But why not 5? well, it is not needed as a cell voltage, and since there is built in power monitoring on the cell phone, then that was what was used.
Because there is no such thing as a 5v battery. The voltage of a battery cell is dependent on its chemistry. The voltage of the assembled battery is an integer multiple of the cell voltage.
There is nothing special about five volts. The battery is not five volts, the components in the phone do not run on five volts. Five volts is only the standard supply on a USB cable, and even that is variable for fast charging. There are voltage conversion circuits in several places in the phone to provide different voltages as required for the requirements of each function.
They could but there are no batteries whose native chemistries produce 5.0V.
What is wrong with the current system, according to you?
What problem are you trying to solve?
If they were, then the charger would need to be 6 or 7V, if that's your beef.