Lithium Batteries and Marine Survey

A lithium bank does not fail a survey for being lithium. Installations fail for being undocumented, unprotected or unfinished — and a conversion is far more likely to be scrutinised than an original factory system, because the surveyor cannot assume anyone qualified specified it.

What a surveyor is assessing

The system, not the battery brand. In practice that means:

• Over-current protection: present, correctly rated for the prospective fault current, and close to the source of power.
• Cabling: sized for the current and the run, marine-grade, properly terminated and supported.
• Mounting and restraint: batteries secured against the motion and impact loads a boat actually experiences.
• Location: ventilation, water ingress risk, heat, service access, and separation from fuel systems.
• Charging arrangements: whether alternator, solar and shore charging are configured for the battery, and whether the alternator is protected.
• BMS integration: what happens when the BMS disconnects, and whether that can disable navigation, steering support, communications or engine starting.
• Labelling and isolation: whether someone unfamiliar with the boat can isolate the system safely in an emergency.
• Documentation: a wiring diagram, manufacturer documentation, and evidence of who did the work.

The most common findings

From the way conversions are typically done, the recurring problems are predictable:

1. A "drop-in" swap with the original lead-acid charging equipment untouched.
2. Unprotected alternator charging, the single most cited technical concern in a lithium conversion.
3. Fusing sized for working current rather than fault current.
4. No monitoring, so nobody can demonstrate the system's state.
5. No documentation at all, which turns every other item into an open question.
6. A BMS shutdown that takes the whole boat with it, including engine starting.

Preparing a conversion for survey or sale

Assemble the pack before it is asked for: as-built wiring diagram, battery and BMS datasheets, the charge parameters configured, fuse ratings and locations, who did the work and under what licence, commissioning notes including tested BMS shutdown behaviour, and photographs taken before the installation was closed up.

An installation with that pack is straightforward to survey. One without it invites the surveyor to assume the worst, and they are right to.

Buying a boat advertised as having lithium

Treat the claim as a starting point, not a specification. A boat advertised with lithium may have anything from a professionally integrated system to batteries dropped into an old lead-acid installation, and the battery brand tells you almost nothing about the installation quality. See used yacht lithium inspection.