Anyone else noticed their LiFePO4 resting voltage behaving oddly in this cold snap?

Been a strange few weeks over here. My 200Ah Fogstar Drift cells have been sitting at around 3.26V per cell at rest after a full charge, which is pretty normal — but the moment temps dropped below about 4°C overnight, they'd settle down to 3.21–3.22V by morning without anything drawing from them. No load, Victron SmartShunt showing near-zero parasitic draw. Just... dropping.

I know LiFePO4 has that famously flat discharge curve and the voltage can be a bit of a liar at the best of times, but this feels like more than the usual noise. Capacity seems fine once they warm up through the day — I'm not losing usable amp-hours in any meaningful way — but it's made my low-voltage alarm trigger twice at 3.20V per cell when the battery was genuinely fine. Had to bump the alarm threshold down a notch, which feels like the wrong solution.

Wondering if anyone else running a similar setup has dialled in a seasonal adjustment to their Victron DVCC settings or just accepts the cold-weather voltage sag as part of life. Got a Multiplus-II 24/3000 feeding the house backup system, so accurate SoC matters more to me than it would in a camper.

KarenEvans | 847 posts | ⭐ Trusted Member

@KevLee yes, completely normal and you'll drive yourself mad overthinking it! LiFePO4 has that notoriously flat discharge curve anyway, but cold genuinely does compress the voltage window further. I've got 280Ah EVE cells in my outbuilding and once it dropped below about 5°C I noticed the resting voltage creeping down to around 3.24-3.25V even after a solid charge.

The chemistry just slows down — the ions aren't moving as freely through the electrolyte, so the cell reads slightly lower at rest than it would at, say, 20°C.

Worth checking your BMS temperature readings if you haven't already. More importantly, are you actually using the capacity and finding it short, or is it just the resting figure worrying you? There's a big difference between a voltage anomaly and an actual capacity loss. 🙂

JX_Boats | 234 posts | ⛵ Member

Same story on my cabin setup last January. I've got Victron BMV-712 monitoring a 280Ah bank and watching the resting voltage creep down with the thermometer felt alarming at first — like something had gone wrong overnight.

What actually helped me was logging voltage alongside temperature for a couple of weeks. Once you plot them together the correlation is obvious and weirdly satisfying. The cells aren't misbehaving, they're just telling you it's cold.

Worth noting: capacity loss is the bigger real-world concern in a static installation. My usable capacity dropped noticeably once the battery shed temperature fell below 5°C. If you're running any meaningful loads off it, that's where you'll feel it before the resting voltage even becomes relevant.

BrookLover | 1,203 posts | 🔋 Battery Nerd

Cold LiFePO4 is basically just a battery cosplaying as a dead battery — mine dropped to 3.19V per cell last February and I nearly ordered replacement cells like an absolute muppet.

BatteryPaula | 412 posts | 🐑 Shepherd's Hut Dweller

My Fogstar cells in the hut spent last winter looking at me like I'd personally offended them every morning — slapped a cheap heat mat under the battery box and suddenly they remembered what voltage was. 🔋🔥

PartnerCamper | 312 posts | ⛵ Member

My boat batteries pulled the exact same stunt last February — nothing like a 3.18V resting voltage to make you question every life decision you've ever made at 6am in a marina. Worth noting that charging below about 5°C is where the real drama starts; @KevLee if your BMS doesn't have low-temp charge cutoff built in, you could be plating lithium internally and that's a gift that keeps on giving (badly). The Fogstar Drift cells are decent but check your BMS spec sheet — my emergency backup setup taught me the hard way that "it'll probably be fine" is not a winter strategy.

LindaPrice87 | 847 posts | 🏠 Tiny House & Boat

Same story on my narrowboat last week — Victron BMV-712 was reading 94% SOC but the cells had visibly sagged under even a modest 20A load. Took me a moment to remember it wasn't the BMS playing up, just physics doing its thing.

Worth noting for anyone with a BMS that has low-temperature charge cutoff: mine kicked in at 5°C and refused charging until I'd run a small load for a bit to warm the pack slightly from within. Actually behaved exactly as intended, just caught me off guard first time.

If you're relying on these as emergency backup, do factor in a thermal management strategy before winter properly bites. Even basic foam insulation around the battery box made a noticeable difference on my setup.

LiFePO4Geek | 1,203 posts | ⚡ Battery Nerd

What you're seeing is perfectly normal LiFePO4 behaviour — the chemistry's internal resistance increases significantly below about 5°C, which causes a sharper voltage sag under any load, making the resting voltage look artificially low. Worth noting that your actual capacity is also temporarily reduced in the cold, sometimes by 20-30% depending how far temps drop.

@KevLee if you haven't already, wrapping the battery compartment with some basic insulation can make a surprising difference — doesn't need to be fancy, even camping foam mat material helps retain the heat generated during charge/discharge cycles.

Ken1999 | 1,203 posts | 🔋 Shed Dweller & Solar Tinkerer

Worth mentioning that LiFePO4 has an unusually flat discharge curve anyway, so even a small drop in OCV can look alarming when you're not used to it. Cold temps genuinely do suppress the resting voltage slightly — the cells aren't lying to you, they're just less chemically "enthusiastic" at low temperatures!

What I'd suggest @KevLee is giving them a proper load test rather than relying purely on resting voltage. Capacity is what matters, and you might find they're actually performing fine once you account for the temperature coefficient. What's your ambient temp in the battery enclosure specifically?