I am building a device using cheap Chinese tablet. One of the problems I have is weak built-in battery. I'd like to replace it with a few 18650 cells.
As far as I know, 18650 cell can be charged up 4V but tablet's source voltage from the built-in battery should not exceed 3.7V +/- 5%.
So, my questions are following: 1) is it true that built-in battery's voltage should not exceed 3.7V +/- 5%? 1.1) if yes, then what are my best options to always have stable 3.7V from 18650 cells? 2) will my tablet's built-in charger manage to charge 3-4 18650 cells connected in parallel?
Thx for your help in advance!