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 barely used my van setup but this year I'm living out of it properly and I've hit a frustrating issue. My 280Ah LiFePO4 bank (four 3.2V 280Ah cells in series, so 12V nominal) keeps having the BMS trip out overnight when temps drop below about 4°C. I'm using a JK BMS, the 200A active balance version I picked up off AliExpress about eight months ago. During the day it's absolutely fine — charging from a 400W roof array with a Victron MPPT 100/30, discharging through a Victron Multiplus 12/1600.

The BMS is throwing a low temperature protection fault, which makes sense — LiFePO4 doesn't like being charged below 0°C and the BMS is set to cut at 5°C charge temp. Problem is it's also cutting discharge, which is leaving me with no power until the cells warm up a bit in the morning. I've got the temp sensor taped to one of the middle cells with self-amalgamating tape, so I'm wondering if it's getting a false cold reading or whether the cells really are that cold overnight.

Has anyone found a reliable way to insulate the battery bank in a van to keep temps above that threshold? I've seen people mention wrapping in closed-cell foam but I don't know how thick you'd need to go to make a meaningful difference overnight. Also curious whether anyone has separated the low-temp cutoff for charge vs discharge in their JK BMS settings — I'm fairly sure it's possible but I don't want to brick anything fiddling with parameters I don't fully understand.

CamperAndrea | 847 posts

@OllieGraham91 Really common issue this time of year! Worth checking whether your BMS has a low-temperature charging cutoff - most decent ones will disconnect at around 0-5°C to protect the cells from lithium plating during charge. That's actually the BMS doing its job correctly rather than failing.

The key question is: does it cut out during charging specifically, or also when you're just drawing power? Discharge is generally fine down to around -10°C with LiFePO4, so if it's cutting under load too, that points more toward a BMS fault or dodgy temperature sensor reading.

Where are your cells located? If they're in an uninsulated space under the floor they could genuinely be hitting those temperatures overnight. A cheap thermometer probe taped directly to a cell will tell you a lot.

RogerRoberts85 | 847 posts

@OllieGraham91 Classic cold weather issue, this. LiFePO4 cells themselves have a built-in protection against charging below 0°C - lithium plating on the anode is a real risk and permanently damages capacity. So your BMS cutting out on the charge side is actually doing its job properly.

Worth checking a couple of things though: what temperature is the BMS actually tripping at? Most budget units are set around 0°C but some trigger as high as 5°C, which is overly cautious. Also, is it cutting discharge as well, or just charge? If it's dropping under load too, that points more toward the cells themselves losing capacity in the cold rather than the BMS protection kicking in.

A cheap solution is a self-regulating heating pad underneath the battery - draws minimal power and keeps everything above the threshold overnight.

LisaHunt88 | 312 posts

Had exactly this with my garden office setup last February. Turned out it wasn't the BMS tripping on temperature — it was actually the cells themselves sitting at a low state of charge going into the cold snap. LiFePO4 internal resistance shoots up when they're both cold and partially discharged, which can trigger undervoltage cutoff rather than a temperature protection event.

Check your BMS logs if it stores them — Victron Smart BMS will show you which protection triggered. That'll tell you immediately whether it's temp or voltage.

Also worth asking: are your cells getting any passive warmth from the van interior, or are they in an external locker? Mine were in an uninsulated box and wrapping them in closed-cell foam made a noticeable difference before I got round to proper heating.

Nobby78 | 1,204 posts

@OllieGraham91 One thing worth checking that nobody's mentioned yet - are your cell-level temperature sensors actually making good contact? I had a nightmare with mine where the adhesive pad had partially lifted off the cell surface over summer, so the BMS was reading ambient air temp rather than actual cell temp. Come winter it was triggering low-temp cutoff way earlier than it should've been because the reading was lagging behind reality.

Quick test - warm the cells up slightly with a heat mat, check your BMS app/display and see if the temp readings respond immediately or seem slow/erratic. That'll tell you a lot.

Also worth noting - what BMS are you running? Some of the cheaper units have fixed low-temp thresholds you can't adjust, whereas others let you tweak the cutoff point in software.

HappyBuilder | 563 posts

Had this exact nightmare on my boat last January. Cells were reading fine on the BMS display but discharge kept cutting at around 5°C ambient.

Turned out my temperature sensor had slipped off its cell and was just floating loose inside the battery box — reading ambient air instead of actual cell temp. Classic.

Worth physically checking the sensor is actually making contact with a cell and ideally taped down with some kapton tape or similar.

Also — if you're not already running a Victron battery protect or a small heating mat wired to a temperature relay, it's worth looking into. Even a cheap seedling heat mat keeps the cells above the BMS low-temp threshold overnight. Sorted mine completely.

LisaHunt88 | 312 posts

Sorry, got cut off there! As I was saying, turned out it wasn't the BMS tripping on temperature at all — it was actually the low voltage cutoff triggering because cold cells have noticeably higher internal resistance, so they sag under load far more than you'd expect. My cells were showing 13.1V at rest but the moment I switched the inverter on, they'd momentarily dip below my BMS's 10V cutoff threshold.

Worth checking your BMS logs if it stores fault codes — mine saved the last trip reason which saved me loads of head-scratching. Also, @OllieGraham91 have you tried reducing your load temporarily to see if it stays stable? If it holds fine on lighter loads but cuts out under the kettle or inverter, that internal resistance issue is almost certainly your culprit rather than a genuine temperature protection fault.

ThingamyBob62 | 847 posts

Had this on my Fogstar cells last February. Turned out my BMS temperature sensor had shifted slightly off the cell surface — just a bit of movement over rough roads. Wasn't getting accurate readings so it was tripping way earlier than needed.

Worth checking the sensor is actually making proper contact with the cell, not just floating near it. I used some kapton tape to hold mine down properly and the phantom cutouts stopped immediately.

Also — what BMS are you running? Some of the cheaper units have really conservative low-temp thresholds set from the factory that you can adjust in settings.

GaryParker97 | 234 posts

Worth checking something nobody's mentioned yet — the cell temperature versus the ambient temperature. In my shepherd's hut build I had my Victron BMV-712 showing the battery compartment at a reasonable 8°C, but the cells themselves were sitting closer to 2°C because they were near an uninsulated floor panel. Most BMS units trip on cell temperature, not ambient. Slap a cheap IR thermometer directly on each cell terminal before assuming the BMS is faulty. Wrapped my battery box in 25mm Kingspan after that — problem completely gone.