Anyone else had their JK BMS trip out in cold weather — or is it just my setup?

Noticed something odd last week when temperatures dropped to around 3°C overnight here in Yorkshire. Woke up to find my whole 12V system had gone dead — inverter, fridge, the lot. Traced it back to the JK BMS (the 200A active balancer version) on my 280Ah LiFePO4 pack having tripped on a low-temp cutoff. Hadn't really thought much about the temperature sensors when I set it up back in summer, so I suspect I've just left the defaults in place and they're a bit aggressive.

I've had a dig around in the JK app and found the "Cell Low Temp Protection" setting sitting at 5°C, which would explain it kicking in at 3°C ambient. Thing is, the cells themselves are inside an insulated wooden box under my bed, so I'd imagine the actual cell temp lags behind ambient by a fair bit — but I haven't got a separate thermometer in there to verify that yet.

Wondering what others are running for their low-temp cutoff settings, particularly for a static cabin or van install in the UK where you're not doing any charging in the cold (solar's basically useless overnight anyway). Is dropping the protection threshold to 0°C reasonable, or am I risking damage to the cells by being too cavalier about it? Any experience with the JK specifically would be brilliant.

@Cleggy51 had almost identical happen in my shepherd's hut last February — woke up to a dead system and initially blamed the Victron MPPT. Turned out the JK BMS had triggered its low-temperature charge protection, which cuts the whole output on some firmware versions, not just charging.

Worth checking two things:

1. What temp threshold is set in the BMS app? Mine was factory-set at 5°C, which is surprisingly easy to hit even inside an uninsulated hut
2. Is it the charge protection or discharge protection triggering? They behave differently

I ended up fitting a small self-regulating heat mat wrapped loosely around the battery — runs off a separate 5A circuit. Solved it completely.

Also worth grabbing the latest JK firmware — there were some odd protection logic bugs in earlier versions that caused nuisance trips above the actual threshold.

@Cleggy51 worth checking whether your JK is actually set to cut at low temperature rather than low voltage — they're separate protection parameters in the app. Mine tripped in my van conversion around 4°C because the low-temp cutoff was still at factory default (5°C I think). Bumped it down to 2°C and it's been fine since, though obviously you're then risking charging below 0°C if you're not careful.

Also — is your battery in an insulated enclosure? Even basic foam lagging made a massive difference to my setup overnight. The cells themselves were reading a degree or two warmer than ambient once I did that.

What capacity/cell type are you running? LiFePO4 handles cold better than other lithium chemistries but it's still not bulletproof.

Hey @Cleggy51, something worth checking — have you got temperature sensors actually making proper contact with your cells? I had a similar head-scratcher with mine and it turned out one of the NTC sensors had worked loose over time, so the BMS was reading ambient air temp instead of the cell surface. At 3°C it would've been right on the edge of the default low temp cutoff anyway. Worth also double-checking your JK app settings — the low temperature charge protection and discharge protection are separate parameters and both ship with fairly conservative defaults from the factory. If you're running LiFePO4, discharge down to around 0°C should generally be fine, though charging below that is a different matter entirely.

@Cleggy51 mine did the same thing last January — turns out my "emergency backup" system spent the whole winter causing emergencies, which feels like a design flaw in my life choices as much as the BMS settings.

@Cleggy51 just to add something nobody's mentioned yet — the JK app (or PC software if you're using that) has a separate low temperature charge protection threshold distinct from the discharge cutoff. Worth pulling up your parameter list and checking both values. I've seen units leave the factory with the charge protection set quite conservatively, sometimes as high as 5°C, which can trigger unexpectedly on a mild autumn night let alone proper Yorkshire cold.

Also, if your battery is sat in an uninsulated space — shed, outhouse, van floor — the cell temperature can lag well behind ambient air by several degrees once you factor in thermal mass. A bit of closed-cell foam around the pack makes a surprising difference and keeps the BMS happy without changing any settings.

@Cleggy51 3°C in Yorkshire is basically the battery equivalent of finding out your mate's "fully charged" phone is at 4% — everything looks fine until it absolutely isn't. My Fogstar cells have a low-temp charge cutoff set in the JK app and I genuinely forgot I'd enabled it until a cold snap caught me out similarly. Worth diving into the Cell Protection settings in the JK app — specifically Low Temperature Protection — because the default values aren't always what you'd expect fresh out of the box, and "discharge protection" vs "charge protection" thresholds are easy to muddle up when you're bleary-eyed at 7am wondering why the kettle's dead.

@Cleggy51 worth checking your low-temperature charge cutoff setting in the JK app — it's separate from the discharge protection. Mine was factory-set at 5°C, meaning any solar or alternator input above that threshold would trigger a protection trip even if discharge was still permitted. Bit counterintuitive. I dropped mine to 0°C on my Ducato build after confirming my Fogstar cells are rated accordingly. Also double-check the MOSFET temperature sensor reading versus ambient — if there's a significant discrepancy, the sensor may have shifted on the board.

@Cleggy51 my Kangoo's LiFePO4 does the same dramatic "I'm dead now" routine the moment it gets a bit nippy — turns out lithium batteries are more Yorkshire than Yorkshire, they absolutely refuse to work below a certain temperature without a strongly-worded argument first. Enable the low temp charge cutoff in the JK settings and stick a cheap self-regulating heat mat on the cells — sorted mine a treat.