Unlike the constant-voltage power supply, the power supply with resistance will have a voltage drop due to its internal resistance, causing the stall current and, therefore, the stall torque to drop with the speed line bottomed to the left.

Internal Resistance of Manganese Dry Cells (1.5V) D cell 0.15 - 0.20 (Ω) C cell 0.25 - 0.35 (Ω) AA cell 0.40 - 0.50 (Ω)

*A motor can be expressed as a generator that produces voltages proportional to its rotational speeds and the in-series resistance across motor terminals.