Is internal resistance a defect in the cell?

The internal resistance of a cell is the resistance of

Three identical cells each of 2 V and unknow internal resistance are connected in parallel. This combination is connected to a 5 ohm resistor. IF the terminal voltage across the cell is 1.5 volt, what is the internal resistance of each cell?

The following circuit shows the use of potentionmeter to measure the internal resistance of a cell.When the key K is closed, how does the balance point change if R is increased keeping current from the driver cell constant?

On what factors does the internal resitance of the cell depend?