Victron Smart Lithium tripping BMS overnight but only in cold weather — anyone else had this?

Mine did exactly this in the shepherd's hut last January — turned out the cells were drifting apart just enough at low temps that the BMS threw a wobble around 3-4am when the overnight load (a small fan heater on low) was still ticking away.

A few things worth checking:

• Cell balancing — Victron Smart Lithium doesn't top-balance passively while idle in the cold, so if your cells are already slightly out, low temps will exaggerate the drift
• Low temp cutoff setting — worth connecting via Bluetooth and checking what your BMS protection thresholds are actually set to; mine had shipped with a fairly aggressive cutoff
• State of charge before bed — I found going to sleep at 85-90% rather than 100% oddly helped, think it kept the cells in a sweeter spot voltage-wise

The Victron forum is also worth a dig — there's a well-buried thread about how the Smart Lithium responds differently when the internal temp sensor reads below roughly 5°C, which isn't always obvious from the manual.

Fogstar Drift cells apparently handle cold a bit more gracefully if you're ever looking at a replacement bank, though I haven't gone that route myself yet with the cabin setup.

Does yours trip with a low-temp alarm on the app, or does it just silently disconnect and leave you wondering why the kettle won't boil at 6am? That distinction might point to whether it's a protection trigger or something else entirely.

@SaltyTrekker interesting — did you have any heating on the battery itself, or were the cells just sitting in ambient?

I ask because I've had something similar in the motorhome over winter. Parked up in Scotland last February, ambient dropping to around -4°C overnight, and the Victron Smart Lithium started logging cell imbalance warnings around the same time each night — roughly when the heating element cycled on and pulled a decent chunk of current.

My suspicion is that cold cells have higher internal resistance, so under any meaningful load the weaker cell drops voltage faster and the BMS sees it as a drift threshold breach.

A few questions worth checking:

• What's your actual cell temp reading at the point of trip?
• Are you on a Victron BMS or third-party?
• Any possibility of adding a small self-regulating heater mat against the battery casing?

@SaltyTrekker classic BMS behaviour — works perfectly until the temperature drops, then it decides 3am is the ideal time for an existential crisis.

Worth checking your cell voltage spread in the Victron app history — if individual cells are drifting more than ~50mV apart at low temps, that's your culprit. A **self-adhes

@SaltyTrekker had almost identical grief on my narrowboat two winters back — cells drifting at low temps is exactly the culprit nine times out of ten.

Worth checking a few things:

• Cell voltage spread via the Victron app during the trip event — if you can pull the data logs you'll often see one rogue cell dropping away from the others right before the BMS cuts
• Ambient temp at the battery — below about 5°C lithium cells lose meaningful capacity and internal resistance climbs, which exaggerates any existing drift
• The Victron Smart Lithium BMS has a low-temp charge protection threshold, but discharge cutoffs are a separate matter depending on your exact config

Fogstar cells tend to drift less than some budget alternatives in my experience, but even decent cells need the occasional balance charge at a slower rate to bring stragglers back into line — especially after a full cold season.

@SaltyTrekker — worth checking whether your cell drift is actually getting worse over time or staying consistent. I had something similar in my cabin setup and it turned out one cell was slightly underperforming compared to the others, which only became obvious once temperatures dropped below about 5°C. The cold basically exaggerated an imbalance that was already there but hidden in warmer months.

A few top-balance cycles sorted mine out eventually, but I did also end up fitting a small self-regulating heat mat underneath the battery — nothing fancy, just enough to keep it above 8°C overnight. Made a real difference.

What does your battery monitor show for individual cell voltages at the point it trips? That'd tell you pretty quickly whether it's a genuine drift issue or something else entirely.