So a bit more explanation here!
There are currently 3 fuses on the board - battery input, debug power input, and DC-DC output. There are also TVS diodes on all 3 power rails for over-voltage protection which shunts power straight to ground which in turn should cause the fuse to blow during a sustained over-voltage.
I don’t expect the TVS to ever trigger, but having an early fuse in case of a short on the battery input is better than having a toasty warm lithium cell.
The debugger power input TVS I might expect to trip due to shenanigans on the debug port, and this one would make sense to be a PTC fuse.
The last fuse and TVS diode is on the output of the DC-DC converter, to prevent 5V appearing on the 3.3V rail if the DC-DC fails short.
Also, the device might end up going for a swim because it will be sticky taped to the back of a boat inside a water-tight case.
