Re: Battery location and venting.
A summary of the ABYC standards:
Not move more than 1 inch with a 90# pull (or 2X battery weight if greater), vertically, fore, aft, and athwart ships.
Ungrounded terminal protected with a boot/shield, in a covered box, or special compartment.
Metallic fuel lines within 12 inches shielded.
Battery not above or below fuel tank.
Here's the quote on vewntillation: "A vent system or other means shall be provided to permit the discharge from the boat of hydrogen gas released from the battery. Battery boxes whose cover forms a pocket over the battery shall be vented. These provisions also apply to sealed batteries"
Mounting surfaces and components can't be of material that's damaged by electrolyte.
Fasteners for battery boxed isolated from areas intended to collect spilled electrolyte.