Anyone else finding their lithium BMS cutting out in this cold snap?

Been having a grief with my 200Ah LiFePO4 bank this past week. Temps have dropped to around -3°C overnight here in the Peak District and my BMS keeps throwing a low-temperature protection fault and shutting down the whole bank. It's a Daly 100A BMS, about 18 months old. Daytime it's fine, but by about 2am the van gets cold enough that it just cuts out and I wake up to no heating and a very unhappy Webasto.

I know LiFePO4 doesn't like charging below 0°C but I wasn't expecting discharge protection to kick in as well. I've got the cells wrapped in some thin foam but clearly that's not doing much. Wondering if I need to add a proper heating mat under the battery, or whether I should just be looking at adjusting the BMS low-temp threshold if that's even possible on a Daly.

Has anyone dealt with this practically? I've seen people mention self-heating batteries but that feels like a big spend when maybe insulation is the answer. What's the cutoff temp set to on yours, and have any of you actually managed to keep a standard LiFePO4 bank happy through a proper British winter without breaking the bank?

LazyMechanic | 847 posts | ⚡ Solar & Wind

@Midge66 Classic winter headache this, mate. The BMS is actually doing its job properly - charging LiFePO4 below about 0°C can permanently damage the cells, so it's cutting out to protect them.

Few things worth trying: a small self-regulating heat tape wrapped around the battery and a bit of closed-cell foam insulation over the top works a treat for keeping temps above the cutoff threshold overnight. Some folk use a cheap reptile heat mat on a thermostat controller.

Longer term, if your batteries are in an outbuilding, even just moving them inside makes a massive difference. Mine are in an insulated box in the utility room now and haven't missed a beat all winter.

What's your setup - are you running any kind of enclosure for the bank at the moment?

NorfolkSolar | Posts: 847 | ⚡ Solar Enthusiast

@Midge66 Classic winter headache, that one! Most LiFePO4 BMS units have low-temp cutoffs set somewhere between 0°C and 5°C to prevent charging damage to the cells - completely normal behaviour actually, it's protecting you from ruining an expensive battery.

The usual fix is insulating the battery box properly - a bit of rigid foam board makes a massive difference. Some folks also run a small self-regulating heat mat inside the enclosure, triggered by a simple thermostat. Keeps things just above the cutoff threshold without much parasitic draw.

Worth checking your BMS settings too - some units let you adjust the temperature threshold, though I'd be cautious about going too low with genuine sub-zero temps.

Where are you housing the batteries - inside or in an outbuilding? Makes a big difference to what solution will work for you.

MoorLee | Posts: 312 | 🔋 Battery Hoarder

@Midge66 Welcome to the glamorous world of off-grid living in Britain, where the sun doesn't charge your batteries AND the cold stops you using them 😄

Seriously though — self-heating LiFePO4 cells are

KangooAdventure | Posts: 1,203 | 🚤 Narrowboat/Motorhome Wanderer

@Midge66 Three winters on the cut taught me this the hard way. Your batteries need insulating before the BMS trips, not after. On my narrowboat I lined the battery box with 25mm Celotex and added a small reptile heat mat (thermostatically controlled, kicks in around 5°C) wired to a separate fused circuit. Total cost was under £40 from Amazon.

The Fogstar Drift cells I switched to last year actually handle cold better than my old budget cells did, but insulation still matters regardless of chemistry.

Worth checking — is your BMS set to cut at 0°C or 5°C? Some cheaper units ship with overly cautious defaults. A Victron BMV will at least give you proper temperature logging so you can see exactly what's triggering the fault rather than guessing in the dark.