Let's just say this comes up often enough for us to comment on it. Johnny comes in and asks, "Can I use 'regular wire' for my boat?" "What about using the leftovers for the RV?".
The answer to this common question is a qualified "yes", if the wire is SAE (Society of Automotive Engineering) J378, J1127 or J1128. All BD Batteries DC Connection wire is J1127 or J1128. These wires are designed for "surface vehicles", not for the special requirements of the marine industry, but meet the minimum standards for boats in limited circumstances. Please do keep this in mind, SAE wire can be up to 12% smaller than AWG wire sizes. To maintain voltage drop requirements (to avoid heat, fires, and inefficiencies) remember to resize those wires. Wires of inadequate size are a very common culprit when troubleshooting a do it yourself wiring project.
Wire Insulation and Water
When a wire runs through a compartment with dripping water, splashing water, or very heavy condensation, the wire should be inside a water tight conduit for safety. Wire Insulation, although waterproof, and airtight when installed, can crack and decay over time. Therefore, all wires should be inspected routinely for such aging and corrosion. Should corrosion be located, the wire should be removed and replaced immediately. With this maintenance in mind, it is easy to see why any wire going through a compartment with water NEEDS TO BE IN A SEALED CONDUIT!
Oil/Fuel vs Standard wire insulation
Standard wire insulation is not designed to be in an area with fuels, oils, diesels, and gasolines. These substances act as a solvent on typical wire insulation, literally wiping it clean off. This can lead to short circuit, sparks, and ignition due to the flammable nature of the liquids. Unless marked "oil resistant" wires should not be run throuh engine compartments, near maintenance activities, or other hydrocarbon rich environments.
Marine Wires are tinned and coated for watertight seal, and corrosion resistance once the seal is permeated. Copper corrodes in water, so a tin coating is applied to the individual strands of marine copper wires. This tinning helps to prevent corrosion but costs more. In addition, marine wires can have a thicker jacket to get the higher "Marine" ratings.