My previous boat, "Glenmore", had a bowthruster with its own battery arrangement all very neatly done up in the bows. Also on its own charging circuit. Only downside, if used, was the decibel level of the thing! Was at Barton Turf one time and a crew mate used it to get out of a bit of trouble! There was a protest swim past by every duck, swan, coot, moorhen and a special delegation from the piscatorial residents!