Anyone else had their BMS cut out in cold weather? Trying to figure out if it's the BMS itself or my cells

Last winter I had my 200Ah LiFePO4 bank (4 x 50Ah EVE cells with a JK BMS) shut down on me twice during cold snaps. Temperatures dropped to around 3–4°C inside the van overnight and both times the BMS tripped out completely — no output, no charging, nothing until I warmed the battery up a bit with a small 12v heating pad. The JK app was showing a low temp protection cutoff, so at least it told me why, but I wasn't expecting it to kick in that early.

I've seen the low temp cutoff threshold listed as 5°C on my JK BMS settings, so technically it's doing its job. But I'm wondering whether it's worth lowering that threshold, or whether that's actually dangerous for the cells themselves. I've read conflicting things — some say LiFePO4 can charge down to 0°C without damage if you keep the current low enough, others say don't touch it below 5°C full stop.

Has anyone adjusted their low temp charge cutoff on a JK BMS and lived to tell the tale? Also curious whether anyone's running a proper battery heating solution — self-regulating heat mats, insulated enclosures, that sort of thing — and whether it actually makes a meaningful difference through a UK winter.

DustyWanderer | 847 posts

@MariaWalker83 Almost certainly the BMS doing its job correctly rather than a fault. JK BMS units typically have a low-temperature charge cutoff around 5°C by default - it's protecting your cells from lithium plating during charging, which can permanently damage them.

Worth checking whether it was cutting out during charging specifically (engine running, solar, hookup) or also under discharge load. If it's discharge-only cutouts at those temperatures, that's less expected and might indicate you've accidentally set a low-temp discharge protection threshold too conservatively in the JK app.

The JK software lets you adjust these parameters fairly easily - many of us running vans in UK winters drop the charge cutoff to around 0°C since LiFePO4 handles mild cold reasonably well during discharge. Adding a small heating pad under the battery helps enormously for overnight drops. What's your charging setup?

LeeParker | 312 posts

@MariaWalker83 Worth checking your JK BMS settings via the app if you haven't already. There's a "Cell Low Temperature Protection" parameter that often defaults somewhere around 5°C from the factory, which would perfectly explain your cutoffs at 3–4°C. You can lower it slightly, but honestly I'd be cautious about doing that without also adding some form of heating — LiFePO4 cells really don't want to be charged below 0°C as it causes lithium plating internally, which is permanent damage.

A small self-regulating heat mat on the battery pack connected through a temperature-controlled relay is a fairly cheap fix. Some people wrap the whole bank in insulation, which at least slows the temperature drop overnight.

What's your charging source — solar, alternator, or mains? That'll affect which scenario actually triggered the protection.

Jonno | 1,204 posts

Had this exact scenario on the narrowboat two winters running before I sorted it. The thing nobody tells you is that LiFePO4 cells don't just dislike charging in the cold — their internal resistance climbs noticeably even during discharge, which can trigger voltage-related cutoffs that look like a BMS fault but aren't really.

What cracked it for me was adding a cheap aquarium heater mat underneath the battery box. Sounds daft, but it keeps the cells just above that threshold overnight using barely any power.

Also worth knowing — 3–4°C is right on the edge of where EVE cells start getting grumpy. A few degrees colder and you'd have had it cutting out much more reliably. So in a perverse way, you're seeing the system work correctly, just at an inconvenient time.

Insulation around the battery box makes a surprising difference too before you spend anything.

GemmaWood | 94 posts

Had almost the same situation with my cabin setup last January. One thing nobody's mentioned — are your cells actually measuring 3–4°C, or is that just the ambient? My cells were sitting a couple of degrees below ambient because they were resting against an uninsulated wall. Once I added some basic foam insulation around the battery box the low-temp cutouts basically stopped.

Also worth asking: are you seeing any charge attempts happening just before the cutout, or is it purely a discharge cutout? My JK was set to cut charging below 5°C but discharge was fine — tripped me up because I had a small solar trickle coming in overnight via a Victron SmartSolar and that triggered it rather than actual load.

Might be worth logging exactly what was happening in the app right before shutdown.

Turbo19 | 847 posts

@MariaWalker83 One thing worth ruling out before you dig deeper into settings — check all your cell interconnect bolts and terminal connections are properly torqued. Cold weather causes contraction in the busbars and can introduce enough resistance to trigger a voltage sag that the BMS interprets as a low cell event, even if the cells themselves are fine. I've seen this fool people into thinking it's a temperature cutoff when it's actually an undervoltage protection triggering under load. Grab a multimeter and check individual cell voltages under load during the cold rather than just at rest. If one cell is reading noticeably lower than the others, you've likely got either a bad cell or a dodgy connection to that cell specifically. Fairly easy to narrow down with a bit of patience.

Lee1963 | 847 posts

@MariaWalker83 Just to add something the others haven't touched on yet — it's worth checking whether both cutouts happened after a period of charging rather than discharging. At 3–4°C you're right on the edge of where LiFePO4 cells really don't want to accept charge current, and some JK units have a low-temperature charge cutoff set quite conservatively from the factory. If your solar or alternator was pushing current in whilst the cells were cold, the BMS would've tripped on that rather than anything being actually faulty. Have a look at your charge low-temp protection threshold in the app — mine was set to 5°C out of the box which caught me out the first winter. Dropping it to 2°C with a heating mat on the cells solved it completely.