Anyone else had issues with Fogstar Drift cells throwing BMS errors in cold weather?

Been running a 200Ah Fogstar Drift LiFePO4 in my shepherd's hut for about eight months now and it's been brilliant until the last few cold snaps. Temps dropped to around 3–4°C overnight and the BMS started throwing low-temperature protection errors, cutting out the load entirely. Heater went off at 2am, which wasn't ideal.

From what I can tell the Drift's BMS cuts charging below 5°C, which is fair enough — that's pretty standard for LiFePO4. But I wasn't even charging at the time, just drawing from it. Has anyone else seen load cutoff happening at these temps, not just charge protection? Wondering if I've got a dodgy unit or if this is expected behaviour.

I've got a Victron SmartShunt on the system so I can see exactly what's happening — voltage looked fine (around 13.1V), nothing weird on the draw side. Was pulling maybe 4A for the heater fan. Just doesn't add up to me why the BMS would trip on discharge at that temp.

Thinking about adding a small self-regulating heat mat under the battery as a workaround, similar to what some van conversion folks do. Has anyone done this on a static install? Curious what you've used and whether you run it on a thermostat or just leave it ticking over.

HeatherOllie | 847 posts

Yes, had almost identical with my Drift pack last February! The BMS was throwing low-temp protection errors around 4–5°C which is actually it working correctly — LiFePO4 cells really don't like being charged below about 5°C as it can cause lithium plating on the anode.

What sorted it for me was adding a small self-regulating heat mat (the kind sold for pipe frost protection) wrapped around the battery and wired to a simple thermostat probe. Keeps it above 8°C overnight for pennies really.

Worth checking your BMS settings too — some have adjustable low-temp cutoff thresholds, though I'd be cautious about lowering them too far. The protection is there for good reason.

@TinaHenderson what BMS are you running with it? Some aftermarket ones are more configurable than the stock unit.

QuietSparky | 1,203 posts

Worth checking what low-temperature cutoff your BMS is configured for — many ship with charging protection kicking in around 5°C, which is actually correct behaviour rather than a fault. LiFePO4 cells genuinely shouldn't be charged below freezing as it causes lithium plating on the anodes.

Practically speaking, a small self-regulating heat mat tucked against the battery (not under it) on a simple thermostat controller can sort this nicely. Set it to kick in around 8°C and your BMS should stop complaining. @HeatherOllie's experience in February backs this up — it's a recurring winter issue for uninsulated installs.

Also worth insulating the battery compartment itself if you haven't already. Even 50mm of PIR board makes a surprising difference in a shepherd's hut. The battery's own minor self-discharge generates a bit of warmth that insulation helps retain.

OldSailor78 | 412 posts

Got a 200Ah Drift in my motorhome and saw similar last winter parked up in Scotland. The charging cutoff is the critical one — discharging at 3–4°C is generally fine but letting the BMS accept charge below ~5°C can cause lithium plating, so it's supposed to disconnect.

What sorted it for me was adding a small self-regulating heat mat (the type used for pipes) underneath the battery, wired to a thermostat probe. Kicks in around 5°C and keeps it just above the threshold overnight on minimal draw.

Alternatively, @QuietSparky is right about the BMS settings — some units let you lower the charge cutoff slightly, but I'd be cautious fiddling with that. Physical heating is a safer long-term fix and costs very little to run.

MoorClive | 634 posts

Good thread, @TinaHenderson. One thing worth adding that nobody's mentioned yet — insulation around the battery itself makes a surprising difference. I wrapped mine in a layer of 25mm Celotex offcuts inside the enclosure and the overnight temps the cells actually see are noticeably higher than ambient. A shepherd's hut loses heat quickly and that battery is essentially sitting in the cold all night.

Also, if you're running any overnight loads (even a small frost stat or trickle to a heater), the gentle self-discharge generates a tiny bit of warmth which helps keep temps above that cutoff threshold. Not a fix exactly, but it buys you a degree or two in marginal conditions.

Long-term, a small self-regulating heat mat on a thermostat is the proper solution — draws very little and keeps the cells happy down to well below freezing.