Comparing quotes on total amp-hours.
Compare on dollars per usable kilowatt-hour, which is chemistry- and voltage-neutral.
Planning
How to Budget a Marine Lithium Battery Conversion
Budget 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.
- Steps
- 6
- Last reviewed
- 4 September 2026
- Independence
- Nobody paid for this page.
Equipment and information required
- Your measured daily amp-hour draw
- The nights you spend away from shore power
How to Budget a Marine Lithium Battery Conversion: steps
Start from usable capacity
Size the bank from your daily draw and your nights at anchor, remembering that you cycle lithium to 80%. That gives the amp-hours you are actually buying.
Price the cases on dollars per usable kilowatt-hour
This is the only figure that compares a 12 V case against a 24 V one honestly. Dollars per amp-hour misrepresents every 24 V battery on the market, because an amp-hour at 25.6 V is twice the energy of one at 12.8 V.
Add the charging path
A DC-DC charger sized to your alternator, an MPPT controller with a true lithium profile if you have solar, and a mains charger that will not float a lithium bank indefinitely.
Add protection and monitoring
A Class-T fuse at each pack's positive terminal, cable sized for the currents the new system can pass, and a shunt-based monitor. These are not accessories on a lithium bank.
Add labour, and ask what it covers
A quote that includes commissioning — charge voltages set, monitor calibrated, a documented wiring diagram — is worth more than one that ends when the cable is landed.
Hold back a contingency for the boat you actually have
Old cable runs, a battery box that will not take the new footprint, and a mains charger with no lithium profile are the three surprises that turn up most often once the panels come off.
Common installation and calculation errors
Related equipment and battery guides
More on planning
How to Plan a Boat Lithium Battery ConversionWork 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.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.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.