Depth finder power and transducer

When mounting a depth finder do you have separate power or to the existing battery? Do most of you mount the transducer in the hull or external?

Most installations are wired upto the crafts battery as they draw very little amps and the transducers are fitted to the inside of your hull,you need to make sure that the transducer is glued to a solid section of fibreglass meaning no foam between two layers of glass.
cheers
jase