It seems like the question of retrofit is of interest, i bought a new hunter 44 that did not have a bow thruster installed by the factory, others i had seen were factory installed. I had a great marine company, reputation considered Alden Yachts, install. And i had concerns about the battery config, etc. i was pleases with the install, but the fiberglass was all over the cabin. but satisfied with the batteries.
The house batteries take the load, but i do monitor the use, i concur 10 amp hours...
yes the option of extra control allows confidence in tight Newport and Edgartown, you can move laterally while moving forward...wheel hard to port, and bow thruster "crawling" the bow starboard you're parallel unparking.
it is a tool, yes, but it's the 21st century.