Fitting a 200Ah lithium bank on a 28ft sailing cruiser — where did you route your cables?

Finally pulled the trigger on a 200Ah LiFePO4 bank for the boat after years of flogging a pair of tired 110Ah AGMs that could barely run the chartplotter and anchor light through a night at anchor. Gone with a Fogstar Drift 200Ah and a Victron SmartShunt to keep an eye on things properly.

The battery itself is sitting in the port cockpit locker for now, which feels a bit rough and ready. Main question is the cable run — I've got about 3.5 metres between the battery and the main fusebox up near the companionway. Running 70mm² tinned marine cable, which should be plenty for the loads I've got (max maybe 80A continuous with the fridge, autopilot, and lights all going). Anyone done a similar run and found a tidy way to get the cable through the bulkhead without it looking like a dog's dinner?

Also slightly paranoid about the locker getting wet — it does take spray in a chop. The Fogstar is supposedly rated for some splash resistance but I'd rather not test that. Has anyone boxed theirs in, or is a vented marine-grade enclosure the way to go? Seen a few people mention making a simple ply box with a drain hole but not sure if that's enough.

Happy to share photos once it's done properly. Just trying to get the cable routing and locker situation sorted before I start making permanent holes.

Not my usual territory — most of my DC cabling experience is in shepherd's huts rather than bilges — but the fundamentals don't change much.

One thing worth flagging specifically for LiFePO4 on a boat: your BMS disconnect under high load can create a voltage spike that'll upset sensitive electronics. Make sure you've got a proper Class T fuse as close to the battery terminals as physically possible, not just an ANL tucked away somewhere convenient.

@SparkySpanner what BMS are you running? If it's a Victron Smart Lithium setup, the VE.Bus BMS has a load disconnect output you can wire to a pre-alarm before it hard-cuts — gives your chartplotter a chance to save state rather than just dying mid-passage.

Cable routing through conduit where it passes any potential chafe points is non-negotiable in a marine environment, regardless of what gauge you're running.

Good thread. One thing I'd add from my garden office install (not marine, granted, but the cable sizing logic transfers) — don't underestimate voltage drop across long runs when you're pulling anchor windlass loads. I ran 70mm² tinned marine cable on a 4m run for my office battery bank and it still showed marginal drop under surge load.

For a 28ft cruiser the battery-to-BMS cable routing through the bilge, are you using tinned copper throughout? Bare copper in a salt environment will corrode at the terminations faster than you'd expect — I've seen horror stories even with heat-shrink solder connectors.

Also worth checking your Victron BMS cable ratings match your fuse sizing before the fuse melts before the BMS trips — common misconfiguration that installers miss.

What's your planned fusing arrangement between the bank and the distribution bus?

Great thread @SparkySpanner! On my Westerly 28 I ran the battery cables from the aft locker up through the bulkhead using a proper waterproof gland, keeping them as short as possible to the BMS. The key thing marine-specific that I'd add — use tinned copper cable throughout, not standard automotive or solar cable. Untinned copper corrodes surprisingly quickly in a salt environment even when apparently protected. I used Belden tinned marine flex and it's made a real difference over the years. Also worth thinking carefully about where your BMS lives; mine is mounted high in the locker, well clear of any potential bilge ingress. A 200Ah LiFePO4 bank will transform your onboard life — running the chartplotter, AIS and anchor light simultaneously will barely touch it!

@KMV_Marine ran mine under the gunwale on the narrowboat — 70mm² all the way, properly sleeved through every bulkhead penetration with grommets that won't turn into cheese graters on your cables the first time you hit a lock sill hard. Keep your runs as short as physically possible; every extra metre is voltage drop you'll be moaning about when the Victron SmartShunt starts lying to you about state of charge. Tinned marine cable is non-negotiable in a wet environment — regular copper turns into a green furry caterpillar faster than you'd believe. Fuse at the battery, not three feet down the run where it's completely useless in an actual fault scenario. Basic stuff but you'd be amazed how many boats I've seen wired like a particularly ambitious toddler had a go with some speaker wire.

Great thread, and congrats on the upgrade @SparkySpanner — you'll wonder how you managed before!

On my Westerly 33 I ran 70mm² from the battery box under the cabin sole, keeping it well away from the bilge water by routing through a raised conduit screwed to the stringer. Every penetration got a proper grommet and a dab of sikaflex round the outside.

One thing worth mentioning that I haven't seen covered yet — label everything at both ends before you button it up. Six months later when you're head-down in a locker in the dark, you'll thank yourself. Also worth thinking carefully about where your ANL fuse lands; I mounted mine on a small fibreglass plate as close to the positive terminal as I could physically get it. Keeps any fault current path nice and short.

Slightly different context here as I'm land-based (garden office and EV charging rather than marine), but cable routing through bulkheads is something I've had to think about carefully too.

One thing nobody's mentioned yet — have you considered where your fusing sits relative to the cable run? On my setup I learned the hard way that having the fuse/breaker as close to the battery positive terminal as physically possible matters enormously, regardless of how tidy your routing ends up being.

Also, what BMS are you going with? On a boat with potential moisture ingress I'd be really curious whether you're looking at something like a Victron SmartShunt alongside it, or relying purely on the BMS display for state-of-charge. The saltwater environment seems like it'd make accurate monitoring even more critical than in my setup.