Anyone else had their JK BMS cut out in cold weather? Losing my mind here

So I've got a 280Ah LiFePO4 pack (4 x EVE 280K cells) with a JK BMS 200A active balancer unit, been running it in my shed-based off-grid setup since last spring. Everything was brilliant through summer — solar input from a 400W array, Victron MPPT 100/30, no drama whatsoever. But since the temperatures dropped below about 5°C here in South Yorkshire, the BMS is randomly cutting the load. No obvious error codes on the app, just drops out.

I've got a temperature probe taped to the cells and they're sitting around 4–6°C when it happens. I know LiFePO4 cells shouldn't be charged below 0°C, but I wouldn't have thought 5°C on discharge should be a problem. I've checked the low-temp protection settings in the JK app and they're set to -10°C cutoff, so it shouldn't be triggering that. Wondering if the probe reading is just inaccurate, or if there's something else going on entirely.

Has anyone else seen this with a JK BMS specifically, or with EVE cells in cold conditions? I'm also curious whether wrapping the battery box in some closed-cell foam insulation would help stabilise the temperature enough to stop this happening — the shed isn't heated. Any thoughts on what to actually check would be really useful.

WillowGazer | 847 posts | ⚡ Off-Grid Enthusiast

@GarySmith58 Oh mate, classic winter BMS headache! Check your low temperature cutoff settings in the JK app — they're often set quite conservatively from the factory, sometimes as high as 5°C charge protection. If your shed is dropping below that overnight, it'll disconnect charging but should still allow discharge.

Worth insulating that battery box too if you haven't already. I wrapped mine in rigid foam board last November and it made a huge difference keeping the cells above the threshold.

One thing people miss — the BMS temperature sensor placement matters enormously. If it's sitting near the terminals rather than actually touching a cell, you're getting ambient readings rather than true cell temp, which can cause erratic behaviour either way.

What temperatures are you actually seeing inside the shed? That'd help narrow it down.

MountainHermit | 2,341 posts | 🏔️ Solar Hermit

@GarySmith58 Been there. My motorhome pack did exactly this parked up in the Cairngorms last January — JK tripped at around 5°C cell temp, wouldn't reconnect until I'd run the diesel heater for an hour.

The JK's low-temp cutoff default is often set aggressively from the factory. Hook it up via Bluetooth and check your Cell Low Temperature Protection setting — mine shipped set at 5°C with a 2°C recovery delta, which is basically useless for a UK winter shed.

I nudged mine to 0°C protection / -2°C recovery. Controversial, but LiFePO4 can discharge at slightly below zero without catastrophic damage — it's charging below zero that kills cells.

Also worth insulating the battery box itself. A sheet of Kingspan does wonders and costs almost nothing.

ExpertBuild | 1,204 posts | 🔧 Off-Grid Builder

@GarySmith58 Worth checking your JK BMS app settings specifically — look at "Cell Low Temperature Protection" and "Cell Low Temperature Protection Recovery." These are often factory-set quite conservatively (sometimes 5°C or even higher), so the BMS is probably doing exactly what it's told rather than malfunctioning. Drop the protection threshold to 0°C and recovery to 2°C if you're not actually charging below freezing, which should stop the nuisance trips.

That said, if your shed genuinely gets below 0°C, don't just bypass the protection — LiFePO4 cells genuinely hate being charged in sub-zero temps and you'll damage capacity long-term. A small self-regulating heat mat under the battery connected to a thermostat is a cheap fix that sorts it properly. About £20-30 all in.

SolarJason | 512 posts | 🔋 Battery Obsessive

@GarySmith58 The bit nobody mentions — JK's low-temp cutoff defaults are conservative from factory, often set around 5°C charge protection. Fine in theory, brutal in a British shed come November.

What sorted mine was wrapping the pack in 25mm Kingspan and tucking a small self-regulating heat mat underneath, wired through a cheap STC-1000 thermostat. Keeps the cells above 8°C overnight without burning much power at all.

Also worth checking whether it's the charge cutoff triggering or discharge — JK logs both separately in the app. Discharge cold protection is usually set lower, so if it's cutting during charge cycles specifically, that narrows it right down to the temperature threshold settings rather than anything sinister with the cells themselves.

BatteryMark | 312 posts | 🔋 Battery Nerd

@GarySmith58 My garden office pack (same EVE 280K cells) did identical last January. The JK has a low temp charge cutoff that defaults somewhere around 5°C I think — perfectly reasonable protection but catches people off guard.

Sorted mine with a cheap self-regulating heat mat wrapped around the pack, thermostatic plug keeping it above 10°C overnight. Cost me about £25 all in from Amazon.

Also worth checking if it's actually the BMS tripping or the cells themselves hitting low voltage under load — cold cells sag badly. Stick a temperature probe on the cells directly rather than relying on the BMS sensor, as those can read ambient rather than actual cell temp depending on placement.