Shown are the power curves for series resistance. R1 is the internal resistance, and R2 is the load.
The right to left axis are the ohms of R2. The vertical axis is the power across the two resistors in amps (one amp per division), and volts for voltage across R2, one volt per division.
As the resistance of R2 is increased from zero, the power and voltage across it begins to climb.
When R2 is equal to R1, half the the power being used is being consumed by each resistor, and the power on R2 is as high as you can get it. As the resistance of R2 continues to increase, the voltage rises across R2, but the power goes down.
This is called the Maximum Power Theorem.
Graph created with Qbasic program, then touched up and added text with image editor.