Anyone else had their Fogstar Drift cells swell after a harsh winter?

Noticed something worrying this week when I went to check on my garden office setup — two of my 280Ah Fogstar Drift cells have developed a noticeable bulge on one face. The battery bank lives in an insulated enclosure outside, but we had a few nights down to -8°C back in January and I'm wondering if that's what's done it.

Running a 4S configuration through a Daly 100A BMS, and the cells were only ever charged between 20–80% SOC as a precaution. Voltages are still reading fairly balanced (sitting around 3.28V each at rest), but the physical swelling is making me nervous about continued use.

Has anyone seen this with LiFePO4 specifically? I know it's more of a lithium-ion problem but these cells definitely weren't like this last autumn. Wondering if the Daly let them discharge too low during a particularly cold snap without me realising — the low-temp cutoff on that BMS isn't the most reliable from what I've read.

Would it be worth reaching out to Fogstar directly, or is swelling on LiFePO4 always a write-off situation regardless of cause?

Mine did the same until I realised I'd been letting them sit at 100% SOC all winter like a plonker — turns out babying them at 80% storage charge is less "paranoid" and more "basic literacy." 🤦

Were they exposed to freezing temps at any point? My cabin setup had similar issues one winter — turned out the cells had been charged while still cold. LiFePO4 really doesn't like that, causes internal damage that shows up as swelling later.

Worth checking if your BMS has any low-temp cutoff. A lot of the cheaper ones don't bother with that protection. Victron kit handles it properly but not everything plays nicely together.

If the bulge is significant I'd honestly not risk using them — Fogstar's support has been decent in my experience, might be worth a message before assuming the worst.

Sorry to hear this @LisaHunt88 — swelling (or "puffing") in LiFePO4 cells is usually a sign of electrolyte decomposition, often triggered by charging at low temperatures rather than storage SOC alone.

Key question: do you have low-temperature charging cutoff enabled on your BMS? If your setup was attempting to charge when the cells were below about 5°C during those cold snaps we had in January, that's almost certainly your culprit. LiFePO4 really doesn't tolerate it.

The bulged cells aren't necessarily dead but I'd treat them with caution — check internal resistance with a proper capacity tester before trusting them with any real load again. Fogstar's customer service has been decent in my experience, worth dropping them an email with photos.

Going forward, a simple cabinet heater on a thermostat set to ~10°C makes a world of difference for winter storage.