Anyone else running lithium in a motorhome that also goes on ferries? Tips for battery isolation compliance?

Finally took the plunge last year and fitted a 200Ah Fogstar Drift lithium under the bed in the motorhome. Brilliant bit of kit, no complaints — but now I'm planning a longer trip to France and Ireland and I'm suddenly having to think about ferry crossings in a way I never did with AGM. Some operators are getting increasingly twitchy about lithium batteries, and the rules seem to vary wildly between Brittany Ferries, Irish Ferries, and the shorter Channel crossings.

The specific thing tripping me up is the main isolation switch situation. Most ferry operators want the leisure battery fully isolated during the crossing, which is straightforward enough — I've got a Victron BatteryProtect wired in already. But is cutting power via the BatteryProtect actually considered "proper" isolation in their eyes, or do they want a physical rotary isolator that crew can operate manually without needing to know anything about your wiring? I've seen both mentioned in various T&Cs but nothing definitive.

Has anyone actually been boarded and inspected, or had a crossing refused? Would love to know whether this is mostly theoretical enforcement or whether they're genuinely checking. Keen to hear from anyone who's crossed regularly with lithium fitted.

Brummie88 | Posts: 847

@MarineVicky nice one on the Fogstar, solid choice! For ferry compliance the key thing most people miss is that lithium falls under a different dangerous goods classification than lead-acid, so just having a battery isolator switch isn't always enough to satisfy the operator.

What's worked for me on Brittany Ferries and Irish Ferries is contacting them directly before booking — ask specifically about "lithium iron phosphate leisure batteries" rather than just saying lithium, as LiFePO4 generally gets a much easier response than they'd give to lithium-ion.

Keep documentation handy showing it's LiFePO4 chemistry, the capacity (200Ah puts you well within most thresholds), and that it's properly fused and installed. Some operators want to see it's got a BMS too.

P&O can be a bit more awkward in my experience, so worth ringing ahead rather than turning up and hoping! 🤞

BerlingoConvert | Posts: 203

Does anyone know whether the rules differ between operators? I'm planning a Stena crossing later this year with my narrowboat batteries (also Fogstar Drift, same as @MarineVicky) temporarily rigged in the motorhome — and I've seen conflicting info about whether a BMS-equipped lithium counts as "isolated" in the eyes of the ferry company, or whether they want a physical disconnect switch as well.

Presumably if the BMS cuts the battery automatically in a fault condition, that should satisfy them — but I've not found anything definitive in P&O or Brittany Ferries' actual T&Cs. Has anyone specifically asked the operator in writing and got a clear answer? I'd rather know before I'm sitting in the boarding queue arguing with a marshal.

LizStewart | Posts: 412

@BerlingoConvert yes, operators do vary — Brittany Ferries and DFDS both ask you to isolate leisure batteries during the crossing, but how strictly they check differs. From personal experience on the Portsmouth–Caen route last summer, the crew were mainly concerned that you could demonstrate isolation if asked rather than doing a full inspection.

Worth printing off your Fogstar's spec sheet showing it has an internal BMS — some operators are more relaxed once they see there's thermal protection built in. Also make sure your isolation switch is accessible and clearly labelled, not buried behind panels.

Irish Ferries apparently have slightly tighter checks on the Dublin route — worth ringing them directly rather than relying on the website FAQ which hasn't been updated in ages.

A decent rotary isolator on the leisure circuit covers you for virtually every operator I've encountered.

JubileeClipHero5 | Posts: 412

Done the Dover–Calais and Portsmouth–Cherbourg runs with lithium in the van. From my experience, operators generally want:

• Main battery isolator accessible and clearly labelled
• BMS documentation to hand if asked (never been asked, but Fogstar provide decent paperwork)
• Declaration that batteries are "installed and not loose cargo"

The distinction they care about is whether it's a fixed installation vs a portable battery — yours sounds compliant as-is.

@BerlingoConvert Stena were actually fine on my Cairnryan crossing, just declared it at booking. Some operators have a tonnage/kWh threshold buried in their dangerous goods policy — worth a quick email before you travel rather than relying on the bloke at check-in knowing his stuff.

Biggest practical tip: fit a proper labelled isolator if you haven't already. Makes any conversation with ferry staff a lot shorter.

T5Wanderer | Posts: 847

Worth noting that some operators specifically ask for a dedicated battery isolation switch accessible without opening panels — not just the BMS disconnect. Brittany Ferries flagged this with me on the Poole–Cherbourg run last summer. My Fogstar setup has a Victron battery protect inline, but the deck crew wanted a physical rotary isolator they could reach quickly if needed.

Fitted a 200A rotary switch in the exterior locker and haven't had an issue since. Costs about £15–20 and takes an afternoon.

Also keep a printed spec sheet for the battery showing it's a proper LFP cell — some staff get nervous about "lithium" in general and having the Fogstar datasheet ready calms things down instantly. Chemistry matters; LFP is considerably safer than other lithium types and worth making that clear.

BirchLover | Posts: 203

@T5Wanderer is right about the dedicated isolator — worth getting a proper rotary switch rather than relying on your BMS disconnect alone. Operators may want to physically see a switch, not trust a circuit board they can't inspect.

I've not done the ferry run myself but I fitted a Victron battery protect on my static setup and it's got me thinking about this for future trips. For a motorhome I'd look at a decent 500A rotary isolator mounted somewhere accessible — near the habitation door is ideal so crew can reach it quickly if needed.

Also worth ringing the ferry operator directly before you travel. Brittany Ferries in particular have been updating their guidance on lithium — better to get it in writing than rely on forum advice (including mine!).

VickyFisher | Posts: 156

Running almost identical setup — Fogstar Drift 200Ah, fitted neatly under the dinette. Did the Holyhead–Dublin crossing last summer and the check-in staff actually asked me to demonstrate the isolator worked before they'd let me board. Caught me slightly off guard if I'm honest.

Worth labelling your isolator clearly too — something laminated that says "Leisure Battery Isolation" with an arrow. The ferry marshals aren't electricians and they just want to see something obvious and accessible. Mine's mounted near the habitation door now rather than buried in the battery compartment.

SolarJunkie | Posts: 2,341

The bit nobody mentions: your BMS disconnect isn't the same as a manual isolator in the eyes of ferry operators. They want a physical break in the circuit, full stop. Victron make decent battery protect units but for compliance purposes a proper manual rotary isolator wired directly at the battery terminal is what satisfies most P&O and Irish Ferries staff if they actually bother checking.

Also check whether your Fogstar Drift is declared as "installed" or "portable" — that distinction occasionally matters on the paperwork. Ran into this nonsense myself crossing to Santander a couple of years back.