Anyone else had their Fogstar Drift BMS throw a fit in cold weather?

Woke up on the narrowboat last week to a flat 12V system at 4°C — Fogstar Drift 100Ah had gone into low-temp lockout overnight and my Victron SmartShunt was just sat there logging the tragedy.

Fair enough that it protects the cells, but I lost heating, the bilge pump, and nearly my sanity. Wondering if there's a way to keep a small load (say a thermostatically-controlled heat pad around the battery) running before the BMS trips, rather than after it's already locked out.

Currently eyeing up a secondary 20Ah AGM just to keep the heating circuit alive as a bodge, but feels like robbing Peter to pay Paul. Anyone cracked this properly?

ValleySoul | 847 posts

@Taffy42 Classic narrowboat winter morning! The Drift's low-temp cutoff kicks in around 5°C for charging if I recall correctly, but discharge protection varies. Worth checking — was your Cerbo or any other load trying to pull charge back through the system overnight? Some kit gets confused about current direction.

One thing that helped me was adding a simple battery blanket insulated against the hull side — canal boats lose a shocking amount of heat through the steel. Kept mine above the threshold through a proper bitter February.

Also, your SmartShunt data might actually be your friend here — you can pull the history and see exactly when the BMS tripped and what the voltage was doing beforehand. Might reveal whether it was genuinely temperature-triggered or something else going on. What does your shunt history show?

Same thing happened to me last winter on the cut.

Worth knowing the Drift will actually charge down to around 0°C if you configure it right via the app — the default low-temp cutoff is quite conservative. Had a play with the settings and it made a big difference.

Also added a small self-regulating heat mat under the battery, wired through a cheap thermostat module off eBay. Kicks on at 3°C, sorts it before the BMS even thinks about locking out. Cost about a tenner all in.

@Taffy42 the SmartShunt logging the tragedy is very relatable 😄 at least you've got good data to work from.

Been there with backup systems in the cold — low-temp lockout is genuinely the silent killer when you're not expecting it.

One thing worth adding: your Victron kit can actually help you prevent this rather than just log it. If you've got a SmartShunt talking to a Cerbo or even just a BMV-712, you can set a low-temp relay trigger to cut charging input before the BMS gets grumpy. Bit of forward planning saves the drama.

Also worth sticking a cheap temp sensor on the battery itself — the cabin air temp can be a few degrees warmer than the battery sitting low in the hull, so 4°C ambient might mean the cells are already at 2-3°C before you realise.

@Jason1970 good point on the actual charge threshold — people assume "cold" means totally dead but it's specifically the charging circuit that locks out first.

MariaJones | 312 posts

My Fogstar Drift on the narrowboat spent last January basically acting like a teenager — completely unresponsive until it warmed up and then pretending nothing happened. 🥶

Stuck a cheap 12V heating pad (the reptile tank kind, embarrassingly) under the battery box and set a Victron relay to kick it on via temperature trigger — problem absolutely solved for about £8 from Amazon. The SmartShunt goes from logging tragedy to logging mild inconvenience instead.

48VNerd | 847 posts

Worth adding to what @Jason1970 mentioned — the SmartShunt won't do anything to prevent the lockout, it'll just faithfully record the whole sorry sequence for you to wince at later.

What's actually helped me is running a small self-regulating heat mat (PTC type) against the battery, wired to a simple thermostat relay set to kick in around 5°C. Draws minimal power and keeps the cells just above the lockout threshold overnight. Victron's low temp cutoff feature in the MPPT settings is also worth configuring as a secondary guard — it stops charge attempts when temps drop, which at least protects the cells even if it doesn't solve the lockout issue entirely.

On a narrowboat you've got the added challenge of damp air making temperature swings feel worse too. Insulating the battery compartment properly made a noticeable difference for mine.