Just a quick story of mine that I thought I would share to highlight that it would be worth just checking stuff out for yourself for piece of mind.
I recently bought a second hand (2008) Signature boat with a Suzuki 90hp 4 stroke on the back and has the dual batts all set up etc.. All starts and runs ok but I noted that when I have pulled up at a spot for a while and restart the motor the sounder and radio would turn off... so yesterday I was checking the connections for the radio and sounder and all looked fine (albeit a bit dodgy)
Anyway a long story short I tracked the wiring back to the batteries only to find that the positive feeds from each battery to the isolator consists of a cable about 5mm in diameter including the insulating... even the link between the negative posts of the batteries is 5mm diameter..
I am amazed that the boat even starts to be honest and am glad that I started looking at why the sounder was switching off as this sort of dodgy crap can turn a good day bad very quickly...
I doubt that this was installed by a dealer as it all looks shonky and requires fresh cables all round...
Pays to look.