VIctron Boat System Troubleshooting Advice Needed

Funny how boat systems and garden office systems share so many headaches — I've been dragged into helping a neighbour diagnose their narrowboat setup this week and it's got me thinking about how differently marine installs behave compared to my land-based stuff.

Their system is centred around a Victron Phoenix Smart 12/3000 (same inverter family I nearly went with before choosing the Multiplus for my office build) and it's been completely dead since they came back from winter mooring. Classic cold-season gremlins.

A few things I'm working through before we power it up again:

• Battery state — they've got AGM banks and I'm suspicious they've sulphated over winter. Resting voltage was showing 11.4V which isn't promising
• VE.Direct comms — want to confirm the Phoenix is actually talking to the Cerbo before we throw load at it
• Shore power history — apparently the marina had some dodgy power events in January, so I want to rule out a blown pre-charge circuit

Has anyone here dealt with Phoenix Smart units that have been sitting dormant for months? Particularly curious whether there's a safe "wake-up" sequence worth following, or whether connecting the Victron Connect app first to check for fault logs is the sensible starting point.

Also — marine installs specifically — do the damp/condensation risks change how you'd approach reinitialising the system? My garden office is sealed reasonably well but a narrowboat engine room is a completely different world.

Would love to hear from anyone who's troubleshot similar Victron boat setups. The more perspectives the better before we start flicking switches.

Boats and garden offices do share a lot of DNA honestly. Main difference I've found is the marine environment absolutely brutalises connections — corrosion on terminals you'd never see in a dry install.

@LindaLamb what's the actual symptom on the narrowboat? Victron stuff usually gives you solid diagnostic info through VRM or even just the MPPT LEDs if they haven't got a Cerbo.

On my tiny house setup I can spot most issues within minutes just from the Victron app — worth checking if the neighbour has that configured. If not, that's step one before poking anything physically.

Also worth checking:

• Battery temp (Fogstar Drift cells hate being charged below 5°C)
• Shore power connection if they're mooring regularly
• BMV readings vs what the inverter thinks

What batteries are they running?

@LindaLamb the narrowboat context is interesting because the charging sources are genuinely more complex than a static cabin setup — you've typically got alternator charging via a B2B (like a Victron Orion-Tr Smart), shore power via a MultiPlus, and possibly solar all fighting over priority simultaneously.

The Victron VE.Bus and VE.Direct don't always play nicely when multiple charge controllers are trying to assert themselves without proper DVCC enabled in VenusOS. Worth checking whether the GX device (Cerbo or CCGX) actually has DVCC switched on — it's off by default and causes exactly the kind of phantom charging conflicts that plague boats.

My cabin setup had similar grief when I added a second MPPT without enabling DVCC first. The BMV-712 was reading nonsense for weeks before I traced it back to that.

@LindaLamb oh I feel this in my soul — spent three confused evenings last autumn convinced my Victron Multiplus was having an existential crisis, only to discover the actual culprit was a corroded negative busbar connection that looked perfectly fine at a glance.

Narrowboats have this wonderful way of hiding faults behind plausible deniability. Everything looks connected. Everything is technically connected. But somewhere in that floating tin can, there's a joint that's developed opinions about conductivity.

@VitoCamper is right about the charging complexity — when you've got shore power, the alternator, solar and a beta engine all potentially arguing over the batteries simultaneously, isolating which source is misbehaving becomes proper detective work.

My first question for your neighbour: what's the Victron app actually saying? Because nine times out of ten, the MPPT or the Cerbo GX has already written a confession — you just need to read it.

@DucatoDream that "three confused evenings" experience is painfully relatable — I've been there with my own backup setup convinced something was fundamentally broken when it turned out to be a single dodgy crimped terminal causing intermittent voltage drop.

For narrowboats specifically, one thing worth checking early is the alternator-to-battery connection quality. Vibration on a boat is constant and relentless — it degrades connections in ways a static garden office setup simply won't see.

Also worth asking: has your neighbour got VE.Connect or VE.Bus Smart Dongle access? Getting proper data out of the Victron kit rather than guessing is half the battle. The history logs often tell you exactly when the fault occurred and what state the system was in beforehand.

What's the actual symptom you're chasing?