By Boat Battery editorial team · 2 minute read · Editorial policy
A Class-T or equivalent fuse at the bank terminal, cable sized for the charger and inverter currents rather than the old lead-acid runs, and terminations you would trust in a seaway.
Battery fault current and fuse interrupt rating
The single most important component in a lithium install is the fuse at the battery terminal, and it is the one most often left out of a quote. LiFePO4 can deliver short-circuit currents in the thousands of amps. A standard marine MRBF or ANL fuse may not interrupt that safely. A Class-T fuse is rated to and is the standard specification on a lithium house bank.
Cable current capacity and voltage drop
Cable is the second problem. The runs on a twenty-five-year-old boat were sized for a bank that could never deliver these currents and for an inverter that did not exist when the boat was built. Size every run for the current the new system can actually pass: the inverter's peak, the DC-DC charger's output, the windlass under load.
Terminations and terminal protection
Terminations matter more on a boat than anywhere else. Crimped, heat-shrunk, tinned lugs, torqued to specification, with no more than four connections on a stud. A loose terminal on a lithium bank is a heat source with a very large power supply behind it.
Parallel battery circuit protection
Finally, every parallel pack gets its own fuse. A bank of three 200 Ah packs with one fuse at the bus is not protected: a fault inside one pack is fed by the other two.
The wiring specification
- Class-T fuse (or equivalent) at each pack's positive terminal
- Cable sized for the highest sustained current, then checked for voltage drop
- Shunt on the negative, between the bank and everything else
- Tinned, crimped and heat-shrunk terminations throughout
- Battery switch rated for the bank's fault current
Related installation planning resources
Use these notes to prepare your own measurements and questions. Check the exact equipment manuals and have the proposed system assessed for your vessel before buying or changing electrical components.
Calculate your boat battery capacity
The house bank calculator takes your loads, your nights on the hook, your solar and your alternator, and returns the bank, the DC-DC charger, the AGM equivalent and the weight you take off the boat.
Open the calculator