Good idea ...fuse in the bow thruster circuit...we don't have one....
Re the battery tester....I got one of these, but its not of much use now as it only works on 12V batteries and I replaced all ours with 3 x 4 banks of 6V 220Ah AGMs.
AND , it really is only a tester for starting batteries...it looks at CCA , not that relevant for a deep cycle bank....but Ill keep the tester, take it home and use it on my tractor !!
SV Elyse SM #437
Blue Lagoon, Yasawa Is, Fiji