What 33 CFR 183.420 actually says
The battery must not sit directly above or below a fuel tank, fuel filter, or fuel-line fitting. Metallic fuel lines within 12 inches and above the battery top need dielectric shielding. Terminals cannot depend on spring tension. Metallic objects cannot contact ungrounded terminals. Hydrogen must be able to leave the boat. We treat those as the install spec, not as optional shop culture.
The bilge is water
A battery standing in bilge water is a short and a corrosion cell. Trays exist to keep the case up, clamped, and dry enough. A milk crate in the lowest point of the hull is not a tray.
Flooded plus a closed engine room
Hydrogen has no odor (Wikipedia). A charger finishing in a sealed engine room is a venting problem. We will not leave a new flooded pack in a box that cannot breathe. AGM reduces spill risk; it does not cancel the fuel-spacing rule.
Cables through wet space
Runs through the bilge need chafe protection and connections that are not hanging as spark points. We secure what we touch. We do not rewire the whole boat unless that is the job you asked for.
On cruisers and Whalers
Engine-room batteries on Sea Rays and console wells on Whalers are the two common tight spaces. We come to the boat in St. Petersburg or Tampa and we look at fuel, vent, and clamp together.
Tools in the well
Ungrounded terminals cannot meet a dropped wrench. We keep the well clear while posts are open, and we put covers back on. That is the metallic-object rule in 33 CFR 183.420 in practice. A tidy well is not cosmetics; it is how a flooded pack in an engine room stays a battery and not a spark gap.
Sources
If this is the job on your boat, see how we replace batteries at the boat. We come to you — Florida towns and counties.