Buying the battery first and working out the charging later.
The charging path decides whether the battery works. Price them as one system.
Planning
How to Plan a Boat Lithium Battery Conversion
Work out your daily amp-hour draw first, size the bank from that, then budget the charging and protection around it — on most boats the hardware around the battery costs between a third and a half of what the battery costs.
- Steps
- 6
- Last reviewed
- 4 September 2026
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How to Plan a Boat Lithium Battery Conversion: steps
Measure what you actually use, not what you own
List every DC load, its current in amps, and the hours it genuinely runs in a day. A 5 A fridge that cycles at 45% duty is 10.8 hours of running, not 24. This number drives everything else, and getting it wrong is the single most common reason a new bank disappoints.
Size the bank before you price anything
Divide your daily draw by 0.8, because you cycle LiFePO4 to 80% rather than flat, then multiply by the nights you spend away from shore power. Credit solar at half its average return so a bank sized on a perfect day still works on the third grey one.
Decide the system voltage now, not later
Twelve volts suits most boats under about 12 m. Twenty-four halves every current in the boat, which makes cable cheaper and inverters easier, but it means new chargers and a converter for 12 V accessories. Changing your mind after the cable is run is expensive.
Budget the charging path as part of the battery
A lithium bank needs a DC-DC charger so the alternator survives, a controller with a real lithium profile, a shunt because the flat voltage curve makes guessing useless, and a fuse that can interrupt what the bank can deliver. Quote these together or the number will move later.
Check compliance before you buy, not after
AS/NZS 3004.2 covers electrical installations on small craft, and your insurer and marina will each have a view. Find out what evidence they want while you can still choose equipment that provides it.
Get the quote itemised
Ask for the bank, the DC-DC charger, the controller, the monitor, the fusing and the labour as separate lines. A single figure hides which corner is being cut, and the corner that gets cut is almost always the fuse.
Common installation and calculation errors
Sizing from the old lead-acid bank's label capacity.
You only ever used about half of that. Size from your measured daily draw instead.
Related equipment and battery guides
More on planning
Is a Lithium Boat Battery Upgrade Worth It? Decision GuideLithium pays for itself where you cycle the bank often and deeply — at anchor, on a liveaboard, or with a fridge running year-round. It rarely pays on a boat that sits on shore power and goes out for a day at a time.How to Budget a Marine Lithium Battery ConversionBudget the bank, then add the charging and protection hardware, which on most boats runs between a third and a half of the battery cost again, then add labour. Compare quotes on dollars per usable kilowatt-hour, not on label capacity.12V vs 24V Boat Electrical Systems: How to ChooseStay at 12 V unless your inverter or windlass currents are forcing cable sizes you cannot run. Twenty-four volts halves every current in the boat, but it means new chargers, a converter for 12 V accessories, and no going back cheaply.