Victron Smart Lithium tripping BMS overnight - temperatures seem fine though

Had something very similar on my narrowboat last winter. Spent weeks convinced it was temperature-related because that's the obvious culprit, but it turned out to be a cell imbalance issue that only revealed itself under low overnight loads.

The BMS was tripping on a low cell voltage deviation rather than overall pack temperature or SOC. One cell was lagging slightly behind the others, and at 2-3am when everything had been drawing slowly for hours, it would finally drift far enough out of tolerance to trigger protection.

A few things worth checking:

• Connect via Bluetooth and log the individual cell voltages over a full overnight cycle — don't just check in the morning after it's recovered
• What's your resting SOC before bed? If you're regularly sitting below 30% overnight, a weak cell will show itself
• Any chance of a parasitic draw you've not accounted for? Even 0.5A continuous adds up across 8 hours

Also worth checking your battery protect settings if you're running one in line — sometimes the low voltage disconnect threshold interacts oddly with the Victron BMS logic and you get a cascade trip that looks like a BMS fault but isn't quite.

What firmware version are you on? There were some known quirks in earlier Victron Smart Lithium firmware around the protection thresholds that got tidied up. Worth checking the Victron community forum too — their support is generally decent at responding to BMS behaviour questions.

Would be interested to hear what your cell voltage spread looks like if you can pull the data. Others on here might have seen the same pattern.

@HeathGazer cell imbalance sneaks up on you like a speed camera on the A303 — by the time you notice it, the damage is done 📸

Worth checking if the trips are happening at a consistent state of charge rather than a consistent time, because overnight discharge curves can mask what's really a voltage divergence issue at low SOC — my Fogstar Drift did exactly this last autumn and the Victron app history made it dead obvious once I stopped staring at the temperature graphs and actually looked at the cell voltage logs.

@HeathGazer this rings so many bells from my static caravan setup. Spent a whole autumn chasing a ghost — logs showed perfectly reasonable temps, BMS kept tripping around 3am, and I was convinced something was haunting the place.

Turned out one of my Fogstar cells had drifted noticeably out of balance. The giveaway nobody mentions: check your BMS logs for the spread between highest and lowest cell voltage, not just the overall pack voltage. Mine looked fine on the surface until I actually dug into individual cell data through the Victron app.

A proper top-balance cycle sorted it completely. Worth also checking your charge absorption settings — if the charger's cutting off too early, weaker cells never get the chance to catch up, and the imbalance compounds over time.

@HeathGazer worth checking whether the trips are happening at a consistent state of charge rather than a consistent time of night. On my setup I was convinced it was temperature-related until I overlaid the SOC logs with the trip events — turned out it was always tripping around the same SOC threshold, which pointed straight to imbalance rather than anything thermal.

If you've got the Victron Connect app, pull up the detailed battery history and look at the min/max cell voltage spread just before each trip. If one cell is racing ahead of the others as you approach full charge, that's your culprit. A proper balancing cycle sorted mine out completely — ran it at a lower charge current for a few days and the spread tightened right up.

@JimWilliams71 good shout on the SoC pattern — that's actually what caught me out on my static caravan setup too. Thought it was time-based (middle of the night, loads dropping off) but it was consistently happening around the same SoC threshold.

Quick question though — are you running the Victron battery protect in the discharge path or just relying on the BMS itself to cut things? I've been wondering whether adding a Cerbo GX gives you enough advance warning via the DVCC settings before the BMS has to do the hard trip.

Also — what capacity are you running? Wondering if a smaller bank is just more sensitive to imbalance showing up as a BMS event because there's less headroom to absorb it before a cell hits its limit.

@JimWilliams71 and @SmartSolarNerd make a good point about the SoC pattern — that's often the giveaway. One thing I'd add: have you checked your battery history in the Victron app specifically for the minimum cell voltage at the moment of each trip?

On my narrowboat I found the BMS was tripping on a single weak cell hitting its low threshold whilst the overall battery voltage still looked reasonable. The overall SoC reading was masking the problem entirely.

If you're seeing trips clustering around a similar cell voltage rather than a time or temperature, that's almost certainly your culprit. A proper balance charge — leaving it on absorption for longer than usual — sometimes sorts minor imbalance, but if one cell is significantly weaker than the rest you might be looking at a warranty conversation with your supplier.