Planning a Lithium Battery Upgrade — Why the Wiring Needs Its Own Plan
Lithium isn't just a lighter, longer-lasting version of the lead-acid bank it replaces — because its internal resistance is so much lower, it can deliver far more current into a fault than lead-acid ever could. That's the part most upgrade conversations skip. A battery bank sized for more usable power pushes more power through the same cables, fuses and switches the boat had before, and if those weren't resized to match, the wiring can be unknowingly inadequate for the bank now sitting behind it — not an inconvenience, but a fire risk sitting in the boat until something goes wrong.
Why More Power Means More Risk, Not Just More Capability
A signed-off scope catches this before it becomes a wiring problem: conductor size, fusing and overcurrent protection calculated for the new bank's actual fault current, not carried over from the lead-acid system it replaced, plus a charging profile and battery management wiring that are correct rather than approximate. Vague scope is refit planning's own most commonly named cause of disputes, and on a lithium conversion vague scope isn't just a pricing risk — it's the gap where an inadequately rated wire or an undersized breaker gets left in place because nobody was specifically asked to check it. A written plan means the fault-current calculation happens once, on paper, before any cable is run — not assumed, and not discovered later.
This isn't a hypothetical. In April 2024, the yacht tender Flagship caught fire at a Miami-area shipyard when its 24-volt lithium-ion battery bank went into thermal runaway. The US National Transportation Safety Board's investigation (report MIR-25-31) found the vessel's battery management system was inoperable, and the crew had been manually charging the bank with a portable charger — bypassing the safety monitoring the system was supposed to provide. The vessel was declared a total loss; no injuries were reported. It's one documented incident, not a trend statistic, and a failed battery management system is a different finding from a fault-current/wiring-sizing problem specifically — but it's a real, investigated example of the same underlying category this page is about: a lithium system that stopped being safely monitored, in a boat, with nobody aware until it was already burning.
Third-party example — not a Maurice Marine job
“Lithium Batteries Blamed for Massive Yacht Blaze,” SY News Ep. 363 — a boating-news recap of the Flagship incident above (YouTube) ↗What We Do
- Upgrade & Refit Planning — the direct answer to this page's search: a written, comparable scope for the lithium conversion, including fault-current-rated fusing and conductor sizing, before installation begins.
- Electrical System Drafting — an updated electrical schematic once the upgrade is complete, so the as-built record — and the actual conductor and protection ratings — match the boat again.
- Electrical System Labelling — new circuits and breakers labelled to match the upgraded system.
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Planning a lithium conversion? Get the wiring and protection sized for the bank you're actually installing, in writing, before anyone touches the boat.
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