Connecting a 12V DC motor to two 9V batteries in series, resulting in 18V, is generally not recommended. The motor, rated for 3V to 12V and designed for applications like air blowers, could run excessively fast at 22,500 RPM, leading to potential overheating and damage. Power consumption increases significantly with RPM, risking the motor's integrity if the load isn't reduced. A better approach is to use a voltage regulator or PWM control to maintain the motor at 12V. Using a single 9V battery may be more suitable given the motor's specifications.