Anyone else had issues with Fogstar Drift cells dropping capacity in cold weather?

I've got four 280Ah Fogstar Drift LiFePO4 cells wired in series (12V nominal, roughly 3.5kWh usable) in my off-grid cabin setup. Running a Daly 100A BMS and charging via a Victron SmartSolar 100/30. Last winter wasn't too bad, but this year we've had a few nights dropping to -5°C or lower and I'm seeing the cells noticeably struggling — capacity feels like it's down maybe 20-30% compared to a warm day, and the BMS is occasionally tripping on low-voltage cutoff around 11.8V under moderate load.

From what I understand, LiFePO4 chemistry just doesn't like the cold — internal resistance climbs and the cells can't deliver current as efficiently. I've read the Fogstar spec sheet and it lists a discharge range down to -20°C, but I suspect that's at a very low C-rate. My load during a cold evening can hit 30-40A briefly (inverter kicking in for the wood burner's fan and some lighting), so I reckon I'm hitting the limits of what cold cells can realistically deliver.

Has anyone fitted a battery heating solution to a similar setup? I've seen the self-adhesive silicone heating mats that run off 12V — considering wrapping the cells and thermostating them to kick in around 5°C. Wondering whether the parasitic draw overnight is actually worth it versus just accepting the reduced winter capacity. What are people doing in practice?

@CrispyMender — LiFePO4 capacity drop in cold is well-documented and almost certainly your culprit rather than faulty cells. Below about 5°C you'll typically see 15–20% reduction; at 0°C it can be 30%+ depending on C-rate.

A few things worth checking:

• Internal resistance — pull a reading from your BMS app at operating temp vs. cold. Elevated IR in the cold will cause the Daly to trip on undervoltage prematurely under load
• Heating — I added a cheap self-regulating heat mat under my cells in my garden office build, thermostatically controlled. Keeps them above 8°C overnight
• Charge cutoff — critically, never charge LiFePO4 below 0°C. Your Victron has a temp-compensated charging profile, make sure the optional temperature sensor is actually wired

What ambient temps are you seeing inside the battery enclosure specifically? The cabin air temp and battery temp can differ significantly.

@BaySeeker is right on the chemistry front, but worth being more precise — LiFePO4 starts losing usable capacity noticeably below about 10°C, and by 0°C you can be looking at 20–30% reduction. Below freezing you also risk damaging cells if you're charging them, which is the bigger concern tbh.

With a cabin setup specifically, insulating the battery enclosure makes a significant difference. I've got my cells in an insulated box inside my tiny house — maintains temps far better than an external store.

Also check your Daly BMS has low-temp charge cutoff enabled. Some units ship with it disabled or set too low. Victron's SmartSolar can be configured with temp-compensated charging if you add a temp sensor, which helps too.

What are your actual cell temps when you're seeing the drop?

@PeakExplorer makes the chemistry point well, but I'd add a practical note from my own setup: internal resistance climbs sharply below 5°C, which means your Daly BMS may be seeing voltage sag under load and tripping low-voltage cutoff before the cells are actually depleted.

Worth logging your cell voltages under load vs. at rest — the spread tells you a lot. If you're seeing more than ~50mV between cells when drawing significant current in cold conditions, that's resistance-induced sag rather than genuine capacity loss.

My fix was insulating the battery enclosure with 50mm kingspan and adding a small self-regulating heat mat wired through a simple thermostat — keeps everything above 8°C overnight. Capacity recovery was almost immediate once ambient temps stabilised. Fogstar Drift cells themselves are solid; cold management is the real variable here.

@CrispyMender one thing worth checking that nobody's mentioned yet — have a look at whether your Daly BMS is physically mounted directly to the cells or somewhere nearby. I made the mistake of mounting mine away from the battery bank thinking it'd be easier to access, but the BMS temperature sensor was reading ambient air rather than actual cell temperature. Meant my low-temp charging cutoff wasn't triggering at the right point, which caused all sorts of confusion when I was trying to diagnose similar symptoms. If the sensor isn't properly in contact with a cell, your protection thresholds won't be working as intended. Worth a quick check before assuming the cells themselves are the problem.