How batteries are recharged ????? what is the reason for battery bulging?

In the currently developed world, everything needs some energy to work. Here, batteries play a major role in storing energy and giving energy to those machines or kinds of stuff.

At first, let us see 

How batteries store energy? 

By fact, batteries are not really storing energies it is a form of energy conversion from one form to other(chemical energy to electrical energy).let's see what is actually happening inside the battery, it consists of two plates anode and cathode. These two plates are separated by an electrolyte which isolates the two plates from each other.

An anode is a positively charged plate that is ready to lose electrons from the plate and the cathode is a negatively charged plate that is ready to accept the electrons from the anode plate.

Ok, you've said that batteries don't store the energy, it is a form of energy conversion. Then, 

How the batteries are getting recharged and discharged?

• Consider that your smartphone is connected to a charger, normally your smartphone's BMS(battery management system) which is known as charge controlling circuit present inside your smartphone it also has a small line of code to perform an inter-communication between your charger and smartphone. 

• The lines of codes decide the voltage and current level to let inside the battery. 

• Even when you put a fast charger to the smartphone which doesn't support fast charging, the software code and the control circuit limits the level of voltage and current from the charger and lets in only the sufficient amount of charge required by the battery.

• so, when the charger is connected to the smartphone the anode(+)positive side of the battery is connected to the positive side of the battery and the cathode(-)negative side of the battery is connected to the negative side of the charger. When the power is given to the charger positive side in the charger attracts the electrons from the cathode in the battery and pushes the electrons to the cathode, therefore, the electrons get stored inside the cathode(-) therefore there is some potential difference produced across the cathode and anode.

This what the actual process running inside your smartphone and battery. 

Your charger attracts the electrons from the anode and pushes to the cathode during this process it creates a potential difference between two electrodes and when the sufficient amount of electrons are stored inside the cathode which ensures the battery is getting charged. 

After charged whenever the load is connected between the battery terminals the electrons flow through the load as a path to reach cathode(+) this flow of electrons is called current and the potential difference between two electrodes ensures the voltage and the loads are getting worked.

This is how your battery is getting recharged and used. 

Let's see the reasons for batteries bulging and weakening.

When anode loses the electrons from it, which leads to creating positive ions in the anode therefore when excess positive ions created it leads to produce heat and evaporates the electrolyte in the form of hydrogen gas when the electrolyte is completely evaporated it leads to short-circuit the two terminals inside and creates more heat. Due to this excess heat and temperature rise batteries are bulged and takes us to the risk of blasting.

So the reason for battery bulging and blasting is not because of late-night overcharging it's because of the aging of battery and increase in temperature inside the battery due to short circuit.