Anyone else had their BMS cut out in cold weather? Trying to figure out if it's a settings issue or just my cells

Last winter I had my 280Ah LiFePO4 bank trip offline twice during cold snaps — both times overnight when temps dropped to around 2–3°C inside my insulated battery box. The BMS (a JK 200A unit) just shut everything down, which left me with no 12V to the heating overnight. Not ideal.

I've been reading that LiFePO4 cells genuinely shouldn't be charged below 0°C, which makes sense, but I wasn't charging at the time — just discharging slowly through a diesel heater controller drawing maybe 3–4A. Seems like the low-temp cutoff was being overly cautious, or possibly my temp sensor is placed badly and reading colder than the actual cell temperature.

Has anyone adjusted the low-temperature discharge cutoff on a JK BMS? Mine's currently set to 5°C which seems quite conservative for discharge-only situations. I've seen people suggest dropping it to 0°C for discharge cutoff while keeping the charge cutoff at 5°C, but I don't want to risk damaging the cells if there's a good reason the default is higher.

Would also be curious whether anyone's added cell-level heating — I've seen the self-heating LiFePO4 batteries advertised but retrofitting a heating mat to an existing bank seems like it could work too. Any experience welcome.

Hey @NickThompson65, worth checking your low temperature charge cutoff setting in the JK app — they often ship with it set around 5°C by default, which would explain exactly what you're seeing. The discharge cutoff is usually set lower (around -10°C) so if it's tripping overnight it's almost certainly the charge protection kicking in, possibly because your solar or other charging source was trying to push current into cold cells.

Try dropping the charge cutoff to 0°C if you're confident your box won't go below freezing, or better yet add a cheap temperature-controlled heat mat inside the box. A small self-regulating heat tape running off a 12V supply sorted mine completely. The JK units are actually pretty configurable once you dig into the Bluetooth app — half the settings aren't obvious at first glance.

@NickThompson65 LiFePO4 cells genuinely hate being charged below ~5°C — the BMS is doing its job, not throwing a tantrum — but if it's cutting discharge too, that's a separate low-temp discharge threshold worth checking in the JK app (usually set around 0°C from factory, which is fine until your "insulated" box turns out to be optimistically named). My Fogstar cells in the cabin survived last winter by wrapping a cheap 20W heat mat around the bank, wired through a Victron relay triggered by a temp sensor — total bodge, works perfectly. Worth noting: 2–3°C ambient means cell surface temp could already be borderline, especially after a cold night with no charge input warming things up.