Anyone else had their BMS cut out in cold weather? Sharing my experience with a 200Ah LiFePO4

Last winter I had a nightmare with my 200Ah LiFePO4 bank (it's a Fogstar Drift if that helps) cutting out completely on cold mornings. Turns out the BMS was doing its job and blocking charging once the cell temps dropped below about 5°C, which I didn't realise was even a thing when I bought it. Spent a whole weekend convinced the battery had died before I finally figured out what was happening.

I've since added a self-heating blanket around the pack and a basic temperature display so I can actually see what's going on. Works a treat now, but I'm wondering if there's a smarter way to handle this — ideally something that only kicks in the heating when needed rather than me manually switching it on each morning. I've seen some BMS units advertised with built-in low-temp charge protection and an integrated heating circuit, but I don't know if they're worth the money or just marketing fluff.

Has anyone wired up a thermostat-controlled heating solution for their lithium bank? I'm thinking a simple 12V reptile mat or something similar on a cheap inkbird thermostat, but not sure what wattage makes sense for a pack this size without draining it overnight. What are other people running in their vans or sheds?

@EmmaPowell74 yeah, been there. My shepherd's hut setup had the exact same issue two winters ago with a 100Ah LiFePO4 — woke up to a flat system because the BMS had locked out charging overnight when temps dropped below about 5°C.

What actually solved it for me was adding a small self-regulating heating pad wrapped around the battery, wired to a thermostat that kicks in around 3°C. Draws minimal power but keeps the cells above the low-temp charging threshold.

Worth also checking your Victron settings if you're running one — you can programme a low-temp charge cutoff in VictronConnect so at least the MPPT doesn't keep hammering a locked-out BMS repeatedly.

The Fogstar Drift BMS is doing exactly what it should, to be fair. It's a user-side problem to solve rather than a product fault.

Finn1975 | 847 posts | ⚡ Solar & Storage Enthusiast

@EmmaPowell74 good that you identified it — so many people assume it's a fault rather than the BMS protecting the cells. One thing worth adding: even if your ambient temps recover during the day, the cells themselves can lag behind significantly, especially if your battery is tucked away in an unventilated compartment. I've got a small 10W heat mat with a thermostat set to kick in around 5°C on my LiFePO4 bank, runs off a separate small SLA just for that purpose. Costs next to nothing to run but means the cells are always ready to accept charge by the time the sun hits the panels. Might be worth considering before next winter rather than waiting for another cutout situation. What temperatures were you actually seeing when it was tripping?

@EmmaPowell74 same thing happened in my static last January — woke up to no power and panicked thinking something had died. Ended up being the low temp cutoff on the BMS doing exactly what it should.

What helped me was adding a small self-regulating heat mat wrapped around the battery. Runs off a tiny bit of 12v draw and keeps the cells above the threshold overnight. Cost me about £15 off eBay.

Also worth checking if your Fogstar BMS lets you see the cell temps via Bluetooth — mine does and it's handy for spotting when you're getting close to the limit before it trips out.

@EmmaPowell74 had this with my setup last February — panels were producing fine but the Fogstar just refused to take charge til gone 10am.

Worth knowing: you can get self-regulating heat pads designed specifically for LiFePO4 banks, runs off a small 12v draw and kicks in automatically below about 5°C. Sorted mine completely.

Also if you're using a Victron MPPT, there's a low temp cutoff setting in VictronConnect — I'd set yours a degree or two above the BMS cutoff so the charger backs off gracefully rather than the BMS having to hard-trip. Saves wear on the BMS over time.