Vent fitting for NG batteries

Interesting one this — I've been down a similar rabbit hole recently with my LDV Convoy camper build, which obviously isn't marine but the same principles apply when you're mounting LiFePO4 cells in an enclosed space.

The vent fittings on the newer Victron NG batteries are worth taking seriously, even if the manual treatment is a bit sparse. From what I can gather, the port is designed for low-pressure passive venting rather than any kind of active extraction — so you're not looking at running a bilge blower or anything dramatic. A simple run of 8mm pneumatic tubing to an exterior fitting should do it, but I'd love to hear from anyone who's actually implemented this properly on a boat where moisture ingress through the vent line becomes a real concern.

My question for the marine folks here: are you running a one-way valve on the exterior end to stop seawater spray or condensation working its way back in? That seems like the obvious solution but I've not seen it documented anywhere officially by Victron. A simple inline check valve from a pneumatics supplier ought to work, though I'd want to confirm it doesn't create back-pressure that defeats the purpose entirely.

Also — has anyone confirmed whether this vent is actually required for warranty purposes, or is it more of a "we recommend this in certain installations" situation? The wording in the SuperPack manual is typically ambiguous on that front.

Would be good to get a few marine installers weighing in. This feels like the sort of detail that gets glossed over until something goes wrong.

@LDVCamper LiFePO4 is your friend here — unlike old lead-acid dinosaurs, they don't off-gas hydrogen during normal operation, so the venting paranoia is largely inherited from a previous era! 🦕

That said, if you're building with prismatic cells and want to sleep soundly, a small passive vent to outside still makes sense for thermal runaway scenarios (rare, but catastrophic when it happens).

On a narrowboat I'd suggest:

• Low-level intake, high-level exhaust — heat and any gases rise
• Keep the BMS accessible — your Victron Smart BMS will thank you
• Avoid sealed compartments entirely if you can

For an LDV Convoy the floor void under a bunk is often the sweet spot — well ventilated naturally and keeps weight low.

Basically: LiFePO4 doesn't need venting, but your peace of mind definitely does. 😄

@RetiredChef is right that LiFePO4 won't off-gas under normal conditions, but "normal" is doing a lot of heavy lifting in that sentence. Thermal runaway is the scenario nobody wants to plan for but absolutely should.

For enclosed spaces — marine or otherwise — I'd still fit a dedicated battery compartment with passive venting minimum, active extraction ideally. A small 12V fan triggered by a gas sensor (hydrogen and CO) gives you belt-and-braces protection.

My cabin setup uses a Victron BMS with the temperature sensor feeding relay logic that kills charging if things get spicy. Overkill? Maybe. But LiFePO4 can vent nasty stuff if cells are compromised.

For the actual vent fittings, look at marine-grade options from Vetus — they're properly sealed against water ingress whilst still allowing airflow. Don't use generic plumbing fittings; they'll let moisture back in and you'll have a different problem entirely.

@DailySolar raises the point I was going to make from bitter experience on my narrowboat.

Had a Fogstar Drift cells build in a poorly ventilated stern locker last summer. Everything behaved perfectly for months — then during a charging fault (Victron MPPT playing up after a firmware update), temperatures crept up and the BMS threw a proper tantrum. Nothing catastrophic, but enough to make me genuinely grateful I'd fitted a small bilge-blower venting that locker to atmosphere anyway, almost as an afterthought.

The key thing on a boat specifically is that gases pool below decks. A van has gravity working slightly in your favour if you vent low. A hull doesn't forgive you the same way.

My rule now: vent every battery compartment regardless of chemistry. The extra 40 quid for a decent 12V blower and some marine-grade hose is proper cheap insurance.

@CharlieThomas — what happened with the Fogstar build? Don't leave us dangling like a half-wired Anderson connector.

My own narrowboat setup taught me that the location of the vent matters as much as whether you fit one at all. I've seen people dutifully drill a hole and fit a nice IP-rated grommet, then route the vent tube downward into the bilge. Hydrogen, being rather famously lighter than air, has opinions about this arrangement.

Route vents upward and outboard — out through the gunwale or cabin top if you can manage it. And fit a proper anti-siphon loop if there's any chance of water ingress back through the tube.

Belts and braces on a boat. The river doesn't care about your theoretical risk assessments.