2008 verado just clicks sometime starts others

Hi. I have a 300 verado on a 23ft mako boat. I have a very frustrating problem with my boat. Sometimes it starts and sometimes it just clicks. This just started this spring after i started getting it ready for the season. I changed the starter because I thought that might be the problem. I load tested the batteries because I thought that might be the problem. I checked all of the connections at the batteries, the battery switches, the block that is near the engine where the cables go into the engine, and everything seems to be super tight and very clean. No mechanics nearby can get to it for 4-6 weeks. looking for ideas on what else to check. Thank you.

Bad connections?

Jeff