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

Running a 200Ah 12V LiFePO4 setup in my shepherd's hut — four Fogstar Drift cells with a Daly BMS. Been brilliant all summer but now we're heading into autumn I'm noticing the usable capacity dropping off noticeably. Sitting at around 160Ah effective on a cold morning (maybe 5°C inside the hut), even after a full charge the night before.

I've got a Victron SmartShunt keeping an eye on things and the SOC numbers look reasonable, but the BMS is cutting out earlier than I'd expect under load. Running a small inverter for a kettle and a 12V diesel heater — nothing mental. Wondering if the Daly is being overly conservative with its low-temp cutoff settings, or whether this is just LiFePO4 doing its thing in the cold.

Has anyone fitted a self-heating solution to their cells, or is the general consensus just to accept the reduced capacity over winter? Seen a few threads about heat mats but not sure if that's overkill for a fixed hut setup rather than a van build.

WattJane | 847 posts

@TerryScott72 Completely normal behaviour with LiFePO4 I'm afraid — they genuinely do lose usable capacity in the cold, it's not your BMS playing tricks. Below about 5°C you can expect to lose 20-30% and it gets worse from there. The chemistry just slows down.

Couple of practical things worth trying: a small self-regulating heat mat underneath the battery bank makes a surprising difference, and keeping the cells inside the hut rather than in an external box helps massively. Also worth checking your Daly's low-temp cutoff settings — some come configured quite conservatively from the factory and will disconnect earlier than necessary.

The capacity does return when temperatures rise again, so at least you're not looking at permanent degradation. How are you housing the bank at the moment?

Gazza25 | 312 posts

@TerryScott72 had exactly this on my narrowboat last winter — anchored up in December and the Fogstar cells were showing maybe 60% of their rated capacity on particularly bitter mornings. The chemistry just slows right down below about 5°C.

What transformed things for me was wrapping the battery box with some 25mm PIR board and chucking a small self-regulating heat mat (wired to a spare Victron relay output) underneath. Barely uses any power but keeps the cells above 10°C overnight.

Worth checking your Daly BMS settings too — many are configured conservatively and will throttle discharge aggressively when cold. Might be cutting you off earlier than necessary.

The cells themselves are fine, genuinely solid kit for the money. It's just a thermal management problem rather than anything wrong with the batteries.

Scouse16 | 203 posts

@TerryScott72 Worth checking what your Daly's low temp cutoff is set to — some of them are configured to disconnect charging below 5°C which can make it seem like you've lost capacity when really the BMS is just being cautious and not letting the cells fully top up overnight. Had a mate with a similar setup in a static caravan and that was exactly his problem. If you can log the BMS data through the app you'll see whether it's genuinely capacity loss or a charging restriction kicking in. Also, are you noticing it more after a cold night or throughout the day? That'd help narrow it down a bit.

GoldenSocket | 1,204 posts

@TerryScott72 Something nobody's mentioned yet — insulation. My garden office setup is in an unheated timber building and I lost far less capacity last winter just by boxing the battery in with 50mm Celotex and adding a small self-regulating heat mat on a thermostat (kicks in below 5°C). Costs pennies to run compared to the capacity you're losing.

The Daly BMS is fine but it won't solve cold — it'll just protect the cells from charging damage. Actual capacity recovery requires the cells staying warm, not just being cut off at low temps.

Fogstar Drift cells themselves are decent quality — I doubt it's a cell fault. Insulate first, then revisit if you're still unhappy with performance come January.

OhmsLaw7 | 1,204 posts

Slap a self-regulating heat mat under the cells — my van setup runs one off a timer before I even wake up, sorted it completely, and the Fogstar Drifts barely notice British winters now. 🔥

Deano13 | 847 posts

This is completely normal behaviour for LiFePO4 unfortunately @TerryScott72 — the chemistry genuinely loses usable capacity as temps drop, it's not a fault. Around 0°C you're looking at maybe 70-80% of rated capacity, and it gets worse the colder it goes. Internal resistance climbs too, so you'll notice voltage sag under load more than usual.

Worth knowing the Drift cells specifically are rated down to -20°C discharge but Fogstar recommend avoiding charging below 0°C full stop — your Daly should be handling that cutoff but double-check it's actually configured correctly rather than just assuming. Some come from the factory with the low temp charge protection either disabled or set too low.

Good shout from @OhmsLaw7 on the heat mat — just make sure whatever you use is LiFePO4-safe and doesn't create hotspots directly against the cells.

SarahLewis | 342 posts

Worth mentioning that charging in the cold is actually more of a concern than discharging, @TerryScott72. Most Daly BMS units don't have low-temperature charge cutoff built in, and charging LiFePO4 below 0°C can cause lithium plating on the anode — permanent damage that compounds over time. Check your BMS spec sheet carefully. If it lacks that protection, you might want to set a low-temp charge cutoff in your charger settings, or look at a BMS upgrade before winter properly sets in. @GoldenSocket's point about insulation will help keep temps above that threshold naturally too.

AshDweller | 89 posts

Running a very similar setup in my shepherd's hut — same Fogstar Drift cells, though I've got a JK BMS rather than Daly. @SarahLewis raises the really important point about charging; have you checked whether your Daly has a low-temperature charge cutoff built in? Some do, some don't.

What's the actual temperature inside the hut when you're seeing the drop? I'm trying to work out at what point it becomes a real problem in practice rather than just on paper — my hut's insulated but it still gets properly cold overnight.