Power wheelchairs can be unique across the various models, but each one has four main components that will appear in every model you find. These are the motor and battery that both allow the wheelchair to run, the drive, and a wheelchair controller allowing the user to steer and otherwise control the chair.
The motors can work with either two-poles or four-poles depending on the power they are meant to exert. Generally, the the more lightweight, two-pole options can carry 250 pounds reliably, whereas the more powerful, heavy duty four-pole options will carry much more weight safely. These heavy duty chairs also require extra strength in other areas. The battery will need to be stronger, as will the engine, wheels, axle, suspension, and frame of the chair.
Power wheelchairs are generally controlled through a joystick or similar device, but some chairs can come with motion-sensitive tubes, screen-based controllers that can read eye-movement, and others options for users who are very seriously impaired. Power wheelchairs are more durable than more lightweight chairs, but are also more expensive, and therefore someone shopping for one will want to look at every detail they can in order to make sure they find something that will last a long time and be worth the cost.