Check out the melted solder and burnt yellow insulation on the yellow crimp connection. ruster.
This shot was taken on board a brand new boat here at the Annapolis sailboat show. The battery shown is one of two that provide power to the bow thruster on a 40 ft. plus sailboat. The melt down shown (look carefully at the yellow crimp connector and the black insulation as well as the puddle of solder under the terminal. As a reminder to all of my regular readers, this is what happens when you try to pull high amps through a loose termination. Lots of heat was generated here. Fortunately the extent of the damage is shown here and since its a brand new boat the terminal and battery will have to be replaced. Make sure that all of your battery terminal connections are clean and free of corrosion and tightened properly to avoid this sort of problem.