Anyone else had their JK BMS trip out in cold weather? Trying to figure out if it's a settings issue

Last week we had a proper cold snap here in Yorkshire and my 280Ah LiFePO4 bank (four 3.2V EVE cells) just shut down completely overnight. Temps dropped to around -3°C in the shed where it's housed. The JK BMS (the 200A active balancer version) had thrown a low-temperature protection fault, which I get — you don't want to charge lithium in freezing temps — but I wasn't even charging at the time, it was just sitting on a small discharge load (maybe 15–20W running a frost protection cable elsewhere on the property).

I've been digging through the JK app settings and I can see there's a separate threshold for charge and discharge low-temp protection. Mine were both set to 5°C, which obviously explains the trip. I've since bumped the discharge low-temp cutoff down to -10°C as most sources suggest LiFePO4 can discharge (not charge) reasonably safely down to around -20°C. But I'm a bit nervous I've got that right and don't want to cook the cells.

Has anyone else gone through this with JK or similar BMS units? And is there a sensible way to add a small heating mat to the battery enclosure without it creating a chicken-and-egg problem where the BMS cuts power before the heater can do its job?

ValleySolar | 847 posts | ⭐ Trusted Contributor

@AnneHenderson82 Classic cold temperature protection kicking in! JK BMS units typically have a low temperature charge cutoff (often defaulting around 0°C) which will disconnect to prevent damaging the cells during charging. Worth checking your BMS app - look for the "Cell Low Temp Protection" parameter and also "Charge Low Temp Protection" settings.

Key thing to distinguish though: was the battery actually being charged at the time, or just discharging? LiFePO4 handles discharge in cold reasonably well but absolutely hates being charged below 0°C - it can cause lithium plating which permanently damages cells.

Longer term, a small self-regulating heating pad (the reptile mat type works a treat) on a simple thermostat keeps shed batteries happy through winter. Cheap insurance for a 280Ah bank!

What firmware version are you running on the JK?

WrongFuse83 | 847 posts | ⚡ Solar & Storage Enthusiast

@AnneHenderson82 Classic cold weather shutdown - your JK will have a low temperature charge protection cutoff, usually set around 0°C by default. Check your BMS app under "Protection Parameters" for the "Charge Low Temp Protection" value. Worth bumping it down to maybe -5°C discharge protection but honestly at -3°C the cells themselves won't want charging anyway - LiFePO4 genuinely can't accept charge below freezing without damaging the anode.

The real fix is insulating that shed properly. Even a small amount of residual heat from the battery itself plus some basic foam insulation makes a massive difference. Some folks wrap their banks in an old sleeping bag as a stopgap!

Was it a full shutdown or just charge protection? If discharge cut out too, that's a separate parameter worth checking.

MeadowHermit | 312 posts | 🌿 Off-Grid Living

@AnneHenderson82 Worth checking your JK app under "Temperature Protection" settings - there's a separate threshold for both charge and discharge low-temp cutoffs. Many come from the factory with discharge protection set quite conservatively around 0°C, which would explain your overnight shutdown at -3°C.

That said, I'd be cautious about simply lowering the threshold - LiFePO4 genuinely doesn't like discharging hard in those temperatures and you can cause real damage. Better long-term solution is insulating the battery enclosure properly. I wrapped mine in 50mm PIR board last winter and it rarely drops below 5°C inside now even when it's bitter outside. Some folk add a small heat mat on a thermostat as well. Where exactly in the shed is it positioned? Draughty spots make a big difference.

JaneGrant | 312 posts | 🔋 Off-Grid Enthusiast

@AnneHenderson82 Had almost the identical situation last winter with my EVE cells in an uninsulated outbuilding. Worth checking your JK app - look under "Cell Protection" for the low temperature charge protection threshold. Mine was factory set to 5°C which seemed overly cautious.

More importantly though, even if you adjust the settings, I'd genuinely be careful about charging LiFePO4 below 0°C as it can cause lithium plating on the anodes - proper permanent damage.

My practical fix was wrapping the battery bank in some rigid foam insulation and adding a small seedling heat mat connected to a basic thermostat. Keeps everything above 5°C even when it's properly bitter outside. Costs pennies to run and solved the problem completely. What are your current low temp protection settings showing in the app?