Reusing the ANL or MRBF fuse from the lead-acid install.
Check its interrupt rating against the new bank's short-circuit current. Usually it does not meet it.
Sizing
How to Choose a Fuse for a Marine Lithium Battery Bank
Fit a Class-T fuse, or an equivalent with a high interrupt rating, at each pack's positive terminal. LiFePO4 can deliver short-circuit currents in the thousands of amps, which a standard MRBF or ANL fuse may not interrupt safely.
- Steps
- 5
- Last reviewed
- 4 September 2026
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Equipment and information required
- Each pack's short-circuit current from its datasheet
- The cable rating of the run it protects
How to Choose a Fuse for a Marine Lithium Battery Bank: steps
Check the interrupt rating, not just the amp rating
The amp rating is when the fuse opens. The interrupt rating is the largest fault current it can open safely without arcing across. On a lithium bank the second number is the one that matters, and it is the one not printed on the front.
Fit the fuse at the source of the energy
The fuse goes at the pack's positive terminal, as close to it as practical. A fuse further down the run leaves the cable between the terminal and the fuse unprotected, and that is the cable nearest the energy.
Fuse every parallel pack individually
Three 200 Ah packs behind one fuse at the bus is not a protected bank: a fault inside one pack is fed by the other two through their own cables. Each pack gets its own fuse.
Match the rating to the cable, not the appetite
The fuse protects the cable. Choose the closest rating to what the cable can carry — oversizing does not protect it and undersizing nuisance-trips. Bigger is not safer here.
Keep separate protection for the branches
The bank fuse protects the main run. Inverters, windlasses and distribution panels each need their own appropriately sized protection downstream.
Common installation and calculation errors
One fuse at the bus for a bank of parallel packs.
One fuse per pack, at the pack.
Related equipment and battery guides
More on sizing
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