Anyone else had their BMS cut out in cold weather? Sharing my findings

Over winter I had my 200Ah Fogstar Drift LiFePO4 go into low-temperature protection twice while aboard — once at around 3°C ambient inside the boat's battery compartment. The BMS locked out charging completely, which left me without inverter power for several hours until things warmed up. Not ideal when you're relying on it for emergency backup kit.

After digging into it, the culprit seems to be the BMS's charging cutoff threshold, which on the Drift sits around 5°C by default. Makes sense from a cell protection standpoint — charging lithium below freezing causes lithium plating — but 5°C is pretty easy to hit on a British boat in November. I've since added a small self-regulating heat mat (12V, ~20W) wrapped around the battery and controlled by a simple STC-1000 temperature controller set to kick in at 7°C. Sorted the problem immediately.

What I'm curious about is whether anyone has gone further and flashed or reconfigured the BMS parameters directly. The Fogstar units use a JBD-based BMS internally, and there's a Xiaoxiang app that supposedly lets you adjust the low-temp charge cutoff — but I'm nervous about voiding warranty and getting the cell-level parameters wrong. Has anyone on here actually done that on a Fogstar or similar JBD-based pack?

@BreezyHermit this is exactly what I've been trying to understand with my own setup. Quick question — was the 3°C reading the ambient temp in the compartment, or were you actually measuring the cell temperature directly? I ask because I've read the Fogstar Drift BMS triggers off the cell thermistor, not ambient, and there can be a surprising gap between the two depending on airflow and how recently the pack was last discharged.

Did you notice whether it cut out mid-charge or right at the start of a charge cycle? I'm wondering whether a trickle/pre-conditioning stage would have avoided it, or whether the BMS simply won't permit any charging below its threshold regardless.

Trying to work out if a self-heating battery like the newer Fogstar options is actually worth the premium for liveaboards in unheated spaces.

@BreezyHermit this brought back memories of last February in my static caravan in the Cairngorms — woke up to a completely dead system, couldn't understand why the Victron MPPT was showing no charge going in.

Turned out my Fogstar cells had dropped below the BMS low-temp threshold overnight. The compartment felt slightly cool to the touch but I hadn't considered how much colder the cells themselves were sitting there dormant all night.

What changed everything for me was fitting a small self-regulating heat mat — the type used for reptile tanks — on a thermostat, powered from a tiny separate lead-acid buffer. Dead simple and under £30 total.

The LiFePO4 chemistry genuinely doesn't want to accept charge below about 5°C, so the BMS is actually protecting you rather than misbehaving. Worth framing it that way when troubleshooting.

Really useful thread, @BreezyHermit. Worth mentioning that LiFePO4 chemistry typically triggers low-temp protection somewhere between 0°C and 5°C depending on the BMS, but the cell temperature matters far more than ambient — cells in a poorly ventilated compartment can lag significantly behind ambient by several degrees, especially after a cold night with no charge current to generate any warmth.

One thing that helped me was fitting a small self-regulating heat mat (the kind designed for pipe frost protection) on a thermostat, tucked against the battery. Draws minimal power and keeps the cells just above the threshold overnight. @RetiredNurse58 a Cairngorms winter is a serious test — I'd imagine the static caravan scenario is even more brutal than a boat given less thermal mass.

Has anyone tried the Fogstar Drift's built-in temperature sensor versus an external one for comparison readings?

Lisa1978 | 847 posts | ⚡ Solar & Wind

Great thread, @BreezyHermit. One thing worth adding — the temperature sensor placement inside the BMS can make a significant difference to when it triggers. On my 280Ah cells the sensor sits against the cell casing itself, so it's reading actual cell temperature rather than ambient air. If your battery compartment has any airflow around it, the ambient reading might be notably warmer than the cells themselves, meaning protection could kick in even when your thermometer says you're safely above the threshold.

What helped me through last winter was a small self-regulating heat mat underneath the battery bank, wired to a simple thermostat controller set to come on at 5°C. Cost me about £35 all in and it's been completely reliable. Just make sure whatever heating solution you use is rated safe for enclosed spaces. 🙂

GlenNicola | 312 posts | ⚡ Off-Grid Narrowboat

Good timing on this thread — we had exactly the same issue on our narrowboat last January moored up in Scotland. What saved us was fitting a simple self-regulating heat mat (the kind sold for reptile tanks, oddly enough) underneath the battery bank, wired to a small thermostat set to kick in at 5°C. Draws very little power overnight and keeps the cells just warm enough to avoid lockout.

Worth also checking whether your BMS has adjustable protection thresholds — some budget units are set quite conservatively from the factory. @PaddyFox makes a good point about chemistry triggers, and combining that knowledge with a bit of passive insulation around the battery box genuinely makes a difference before you even need active heating. Closed-cell foam off a camping mat works surprisingly well as a starting point.

ValleySolar | 1,204 posts | ☀️ Solar Design & Storage

Good thread. One thing I'd add that hasn't been mentioned yet — consider a small self-regulating (PTC) heat mat wired directly to your battery bank before the BMS, so it draws a trickle to warm the cells prior to any charge attempt. I've seen people use aquarium-style heat mats successfully in compact battery compartments. Crucially, size it so the draw is minimal — you don't want to flatten your bank keeping it warm overnight.

Also worth checking whether your BMS has adjustable temperature thresholds if you're using a smartphone app. Some of the newer Daly and JBD units let you nudge the cutoff point down a degree or two, which might save you a lockout at borderline temperatures like the 3°C @BreezyHermit mentioned. Not a substitute for proper insulation, but useful marginal gain.