Bow and stern thrusters whether retractable or tunnel require a power source. On a yacht this can be either a 12/24V DC (electric) motor or a hydraulic motor.
The hydraulic motor will need to draw power from a thermal engine (via a hydraulic pump) or a remote mounted DC motor (also via a hydraulic pump).
The DC motor will draw power directly from a battery bank.

The choice of power will depend on factors such as frequency of use, runtime required, and thruster size needed.