Anyone else had grief with JK BMS low-temp cutoff tripping in winter van life?

Picked up a 200Ah LiFePO4 from a well-known Chinese brand back in September and fitted a JK BMS (the 200A active balancer version). All was fine through autumn but now we're into proper cold weather I'm getting nuisance cutoffs overnight when temps drop. Last night it tripped at around 4°C according to my Victron BMV-712, which seems way too conservative — I've got the low-temp charge cutoff set to 5°C in the JK app but I'd have thought the battery itself would be fine to discharge at that temp?

From what I can gather, the JK is cutting discharge as well as charge once it hits that threshold, which isn't what I want at all. I need the heating to keep running overnight (Webasto Thermo Top Evo, pulls about 8-10A) otherwise the van gets absolutely miserable by morning. Bit of a catch-22 situation — the heating needs the battery, but the BMS won't let the battery run because it's cold.

Has anyone found a reliable way to separate the charge and discharge low-temp settings on the JK firmware? I'm on v11.25 and the app seems to lump them together, though I've seen hints in older threads that newer firmware handles it differently. Alternatively, is there a wiring workaround people have used — like bypassing the BMS for the heater circuit with an inline fuse directly off the cells?

@SomersetCamper had this exact problem on my shepherd's hut build last February. Woke up to a dead system at -4°C — JK had tripped the low-temp cutoff at around 5°C charge protection.

Few questions before anyone gives you the standard advice:

• What have you set your charge low-temp cutoff at in the JK app? Factory default is often too conservative
• Are your cells actually cold or just the BMS sensor reading cold? Sensor placement matters massively
• Do you have any insulation around the battery itself?

The JK app lets you adjust the threshold but there's a balance — LiFePO4 genuinely doesn't want charging below 0°C or you'll get lithium plating. Have you considered a self-heating battery instead, like the Fogstar Drift range? Designed specifically for this kind of scenario.

What temperatures are you actually seeing inside the van overnight?

@SomersetCamper the JK's low-temp cutoff default is usually set conservatively around 5°C — crack open the JK BMS app (Bluetooth icon, bottom right) and you'll find Cell Low Temp Protection under the protection parameters; I've got mine dialled to 0°C charge cutoff with a 2°C recovery, which stops nuisance trips whilst still protecting the cells from genuine cold-charging damage.

Worth noting: discharge at low temps is generally fine for LiFePO4, it's charging below 0°C that destroys capacity — so make sure you've got separate charge and discharge cutoff thresholds set, not just one blanket temperature limit.

If your van idles regularly, a small self-heating pad on the battery (Fogstar sell suitable ones) triggered off a temperature relay solves the root cause rather than just fiddling with BMS tolerances.

@SomersetCamper yeah the JK low-temp cutoff is set pretty aggressively from factory — think it's around 5°C charge cutoff by default.

Worth connecting via the JK app over Bluetooth and bumping the charge low-temp protection down to about 0°C if your cells can handle it. Most decent LiFePO4 can take a light charge at 0°C without drama.

Also fitted a self-heating cable wrap around my pack last winter — dirt cheap off Amazon and runs off a small DC timer. Sorted it completely.

One thing to double-check: make sure you're not confusing charge cutoff with discharge cutoff — discharge can go lower, around -20°C on most LiFePO4. Fogstar cells are pretty cold-tolerant in my experience.

Hey @SomersetCamper, worth checking your low-temp charge cutoff parameter in the JK app — mine shipped with it set to around 5°C which is quite conservative. I nudged mine down to 0°C since LiFePO4 can technically accept a slow charge just below freezing without serious damage, though I wouldn't push it further than that. More importantly, have you considered a small self-regulating heat mat on the cells? I picked up a 12V silicone pad from Amazon for about a fiver and wired it through a cheap thermostat module — kicks in at 2°C and keeps the pack above the cutoff threshold overnight. Makes a real difference in a van where ambient temps can drop fast. The JK protection itself is doing exactly what it should, so I'd work with it rather than just raising the threshold blindly.

@SomersetCamper one thing worth adding to what the others have said — even after you've adjusted the cutoff threshold in the JK app, make sure you're also setting a reasonable recovery temperature (usually a couple of degrees above the cutoff). Without that gap, you can end up with the BMS rapidly cycling on and off if temps are hovering right at the limit, which isn't great for anything connected.

Also worth insulating your battery box properly if you haven't already — even a bit of Celotex or plain foam board makes a surprising difference overnight. The cells themselves generate a small amount of heat during discharge which helps too. I ran a 12V setup through a Scottish winter and decent insulation kept my pack several degrees above ambient most nights.

Good shout from @ExTrucker63 there. One thing I'd add that nobody's mentioned yet — consider fitting a small self-regulating PTC heat mat directly to your cells if you're regularly parking overnight in sub-zero temps. They draw very little current and can keep your pack above the cutoff threshold passively. I ran a 12V 20W pad on my 100Ah setup last winter, wired through a simple thermostat controller set to kick in around 3°C. Made a massive difference and the BMS barely blinked all season. Just make sure whatever you use is rated for direct contact with lithium cells and isn't creating any hotspots. Worth the tenner or so it costs rather than waking up with a dead pack.