Victron Smart Lithium tripping BMS overnight but only when it's cold

Had exactly this on my narrowboat last winter — woke up to a dead boat twice before I figured it out.

The culprit in my case was low-temperature cutoff on the BMS triggering during early morning dips, not an actual cell-level fault. The Victron Smart Lithium has a built-in low-temp disconnect that kicks in around 5°C by default to prevent charging damage. If your charger (shore power, alternator, solar — anything) is still pushing amps into the battery when the cells drop below that threshold overnight, the BMS protects itself by tripping.

Worth checking a few things:

• VictronConnect app → look at the battery history log. It'll show you whether it's a low-temp event or an undervoltage/overcurrent trip. These are very different problems with very different fixes.
• Are you running a Victron Battery Protect or relying solely on the Smart Lithium's internal BMS? The latter will disconnect everything including loads, which explains waking up to a dead system.
• What's your ambient temperature in the battery compartment? On my boat the bilge drops well below air temp when we're moored with no heating running.

My fix was fitting a small battery box with a 12V heat mat (thermostatically controlled, draws almost nothing) and setting it to maintain 8°C minimum. Problem completely gone since.

Also check your BMS isn't flagging a cell imbalance — cold temperatures exaggerate imbalance, so a borderline cell that looks fine at 20°C can trip the BMS at 3°C.

What temperatures are you seeing and what does the history log say? That'll narrow it right down.

@YorkshireBoater good shout on the low-temp cutoff — worth adding that the Victron Smart Lithium batteries have a built-in low-temp disconnect at around 5°C, which is separate from any external BMS protection. This catches people out because they assume one cutoff and don't realise there are potentially two layers triggering.

On my static caravan setup, I solved the overnight cold issue by adding a Victron Smart BMS 12/200 alongside a small self-regulating heating pad (the type sold for reptile tanks, ironically) taped to the battery casing, powered from a tiny dedicated circuit. Keeps the cells above 8°C even in a Devon winter.

Also worth checking — is your battery temperature sensor actually connected and reporting correctly to the Cerbo/GX device? A disconnected sensor can cause the system to assume worst-case temperatures and trip unnecessarily.

Good thread, this one. Worth flagging something @YorkshireBoater and @DevonDweller might not have mentioned — the charge disconnect temperature and discharge disconnect temperature are separate thresholds on the Victron Smart Lithium BMS. You can have a situation where the battery happily runs loads overnight but then the charger (shore power, alternator, solar) tries to push charge in at 4-5°C and triggers a fault that looks like a full shutdown.

On my narrowboat I solved this by setting the Cerbo GX to pause charging below 8°C using a temperature-compensated relay — keeps the loads running without the BMS getting confused.

Also check your VE.Bus System Configurator for the "allow to charge" flag — if that's being pulled low by the BMS protect signal it'll cascade into a full trip even when the battery has plenty of capacity left.

Great thread. One thing nobody's touched on yet — cell imbalance gets dramatically worse in the cold. A pack that looks balanced at 20°C can show a 50-100mV spread at 2°C, which trips the BMS even when the average SOC looks fine.

Worth connecting via Victron Connect and watching individual cell voltages overnight if you can. I did exactly this on my motorhome last January, parked up in the Cairngorms like an idiot, and watched cell 3 dive off a cliff while the others held steady.

Turned out one cell had slight capacity fade — never showed up in summer. Cold just exposed it brutally.

Before assuming it's purely a temperature cutoff issue, @YorkshireBoater, I'd rule out a rogue cell first. A Fogstar Drift replacement cell sorted mine, though fitting it yourself obviously voids warranty considerations.