For goodness sake, just get a new battery.  Why even consider why.  If its 5 years old, you could do with a new one anyway. 

4 hours ago, lopburi3 said:

I am well aware of that - you might want to read this as it is very important to maintain Li-ion batteries within a normal charged range.

https://www.scienceabc.com/innovation/does-letting-a-phone-discharge-completely-before-charging-it-again-improve-its-battery-life.html

 

Yes but if you continue charging them every time you get home even if they dont need charging it will affect them. We used to suffer with that with the site radios. Every so often we had to condition the batteries. Operators would take a radio and go to site then as soon as they returned straight into the charger.

35 minutes ago, upu2 said:

Yes but if you continue charging them every time you get home even if they dont need charging it will affect them. We used to suffer with that with the site radios. Every so often we had to condition the batteries. Operators would take a radio and go to site then as soon as they returned straight into the charger.

I suspect you are thinking of NiCd type battery memory effect.  That was real and a problem with mobile VHF radios we used to have to use for communications - you did need to discharge and charge occasionally to prevent.  But that is not the case with today's phone batteries.  

Deleted due to lack of humor on OP part

11 hours ago, lopburi3 said:

I suspect you are thinking of NiCd type battery memory effect.  That was real and a problem with mobile VHF radios we used to have to use for communications - you did need to discharge and charge occasionally to prevent.  But that is not the case with today's phone batteries.  

In theory NiCd do not suffer from memory effect. They do however suffer for other effects which have the same overall problem