Anyone else had their BMS cut out in cold weather? Trying to work out if mine's faulty or just doing its job

I've got a 200Ah lithium (LiFePO4) pack I built myself using EVE cells, with a JK BMS set to cut off at 5°C. Last week we had that cold snap and the van was sitting outside overnight — woke up to find the BMS had tripped and I had no power at all. Temperatures got down to about 2°C according to my weather station, so technically it did exactly what it's supposed to do. Still caught me off guard at 6am though.

My question is really about whether people bother adjusting that low-temp cutoff, or just leave it at the factory default. I've read that charging below 0°C is the real danger for lithium cells, but discharging at low temps is apparently less of an issue — at least down to around -10°C or so for LiFePO4. So I'm wondering if the cutoff being at 5°C is overly cautious for discharge, even if it makes sense for charging.

Has anyone split their charge and discharge low-temp thresholds on a JK BMS? I can see there are separate parameters for it in the app but I've not touched them yet and don't want to do anything daft. Keen to hear what settings others are running, especially those of you who use your vans or off-grid setups through a proper British winter.

@Maria1963 that's your BMS doing exactly what it should — LiFePO4 cells can't safely accept charge below around 5°C, you'll plate lithium on the anode and permanently damage capacity. Not a fault at all.

My static does the same on cold mornings with my Pylontechs — they have low-temp cutoff built in too. Annoying but better than a ruined pack.

Few options worth looking at:

• Self-heating cells (EVE do a version)
• A small heat mat under the battery controlled by a thermostat
• Adjust your BMS to allow discharge below 5°C but keep charge cutoff — JK lets you set those independently

Worth checking your JK settings actually — charge and discharge low-temp thresholds are separate parameters. Discharge is generally fine down to around -20°C with EVE cells.

Been through exactly this with my own build last winter! @Maria1963 just to add to what @Pylontech_Wizard said — it's worth noting that discharge is still fine at low temps, it's specifically charging that causes the damage. Lithium plating on the anode is the issue — irreversible and cumulative, so your BMS is genuinely protecting your investment there.

What I did as a workaround was fit a small self-regulating heating pad underneath my pack, wired to a separate lead-acid leisure battery. Brings the cells up to temperature before the solar or hook-up kicks in. Costs pennies to run and means I'm not losing charging hours on cold mornings. Might be worth considering if you're regularly parked up in the cold overnight.

@Maria1963 just to add a practical angle here — even if the BMS has protected you from charging, you can still use power from the pack in the cold, it's only charging that's the real risk. So worth checking your BMS settings distinguish between charge and discharge cutoffs if yours supports that. The JK does allow separate thresholds which is handy.

One thing worth doing once things warm up is checking your cell voltages are still balanced — sometimes if a partially-protected cutoff happened mid-charge you can end up with a bit of drift between cells. Nothing dramatic usually, just worth a look.

Long term, some folk add a small self-regulating heating pad underneath the cells, wired to come on before charging starts. Makes cold mornings much less of a headache in a van setup.

What @Gibbo said about still being able to draw power is worth remembering — I've woken up on the narrowboat to a similar situation more than once. The BMS cutting charge was the least of my worries; it was the heating circuit that needed the power I couldn't replace until things warmed up.

One thing I'd add: once the cells crept back above 5°C on mine, the JK didn't always reconnect automatically without a small load applied first. Might be a settings thing, but worth knowing before you're standing there in the cold wondering why the pack's still showing "protected" at 8°C. Check your reactivation threshold in the JK app — there's a small hysteresis setting that can catch people out.

Something worth adding that hasn't been mentioned yet — if you're regularly parking outside in winter, it might be worth insulating the battery compartment a bit. Even just some rigid foam board around the sides makes a surprising difference to overnight temps. I've got my EVE cells in a wooden box with 25mm PIR insulation and they hold heat from the day's usage well into the night. The cells themselves generate a tiny bit of warmth during discharge too, which helps.

Also worth checking your JK settings — some firmware versions let you set separate charge and discharge low-temp cutoffs, so you could potentially tighten the charge cutoff while keeping discharge available lower down. @Maria1963 sounds like your BMS did exactly what it should though, so don't panic!

Good point from @Turbo34 — I've gone a step further on the boat and wrapped my battery compartment with a bit of 25mm PIR board. Cheap from any builders' merchant and makes a surprising difference to overnight temps.

The JK BMS at 5°C is doing exactly what it should though, @Maria1963. LiFePO4 cells don't take charge below 0°C without risking lithium plating — 5°C gives you a sensible buffer. Some people drop their cutoff to 2°C but I wouldn't go lower than that with EVE cells.

Worth checking your JK app logs to see what temperature it actually tripped at — you can confirm whether it's reading accurately or if the NTC sensor placement is giving you odd readings. Mine was logging falsely low temps until I repositioned it away from the hull side.

@DevonBoater that PIR trick is genuinely clever — passive insulation doing the heavy lifting before any active heating kicks in.

My own story on this: I had my EVE cells sitting in a steel-framed compartment under the van floor last February. Coldest night of the year, woke up to the same dead-silence scenario you've described. Turned out the BMS was doing exactly what it should — cells were reading 3°C.

What changed everything for me was fitting a small Victron temperature sensor logging overnight lows. Once you see how fast an uninsulated steel box loses heat, you stop questioning the BMS and start questioning your installation.