A battery switch like that is two terminals and a spring-loaded bar that switches between them, almost every problem with battery equipment is the terminals, connectors, the wire or combination of any of the above.
P, You could have provided photos of the damage. Who installed the switch?
And I think you said three years its been in, is that the last time any of the battery terminals in your boat where checked? What is the electrician friend's place in all, this did he burn it out?
customer coddling service is a thing of the past, that went out with the baby boomer perception that "Sears" will replace anyting no questions asked"
The customer is no longer always right.
I provided the PDF, wonder if anybody actually read it. The warranty is basically no warranty, free of defect from the factory.
People like me in contracting business most of their lives are painfully aware that warranty and guarantees are not "law" there are a good faith option.
Seems pretty standard, they warranted only defects in manufacturing not improper installation or maintenance.
The OP stated that the switch was rated in excess of 300 amps, while technically true for the one he pictured it is actually only rated for 250 amps continuous and 360 amps for 5 minutes, intermittent, per PERKO's website and specs listed there. This could mean two things one occasionally it will work at 360 amps for 5 minutes, probably not IMO, or more likely it will work at 360 amps for up to 5 minutes if the draw is intermittent, in other words not continuous and is given a chance to cool down. I would never claim a switch was rated for its max intermittent current, I personally would only say the switch was rated for 250 Amps max not the 360 amps. Now if the OP was using the Heavy Duty ones they are rated at 450 amps continuous and 1200 intermittent, but they do not mach the picture provided.
Lots of manufacturers do this try returning a desktop motherboard with an Intel socket in it after a CPU was installed for a bent pins... No manufacturer takes them back after a cpu was installed that I know of.