Are the breakers in your home at the source (breaker box) or supply (wall socket)?
Breakers trip on downstream faults. Without the fuse on the battery that wire could ground and burn w/o tripping the breaker. The breaker protects the wire from the breaker to the panel
The head scratcher is the breaker. I can only assume they used it as an on-off switch. A simple in-line toggle switch is all that was needed to perform that action
