Does battery capacity drop noticeably in winter? Seeing odd readings on my 200Ah LiFePO4

Over the past few weeks I've noticed my 200Ah LiFePO4 (it's a Fogstar Drift) sitting in my van behaving a bit strangely. The BMS is showing what looks like a lower usable capacity than I'd expect — I'm maybe getting 160-170Ah before it starts cutting off, whereas in summer I was comfortably pulling the full amount. Temperatures overnight have been dropping to around 3-5°C in the garage where the van lives.

From what I understand, LiFePO4 is supposed to handle cold better than standard lithium, but I wasn't expecting this much of a drop. My setup is a Victron SmartShunt keeping track of things, and the SOC readings seem to drift a bit too — sometimes it'll show 40% and then the BMS cuts out unexpectedly. Not sure if that's a calibration issue or something more fundamental going on.

Has anyone else seen this kind of capacity reduction in colder months? I'm trying to work out whether this is just normal chemistry behaviour I should stop worrying about, or whether there's something worth investigating properly. Also wondering if the charge voltage from my Victron MPPT needs adjusting for winter — currently set to 14.2V absorption, 13.6V float.

EdMason | 847 posts

@Graham1995 LiFePO4 is actually much better than lead-acid in cold temps, but it's not immune. Below around 5°C you'll definitely see some capacity reduction — typically 10-20% at 0°C, potentially more if it's genuinely freezing in that van overnight. The chemistry just slows down.

Worth checking: is your BMS showing reduced capacity during use, or just on the resting voltage readout? LiFePO4 voltage curves are notoriously flat anyway, so BMS SOC readings can be a bit unreliable at the best of times. The Fogstar Drift should handle cold reasonably well, but if the cells themselves are cold when you're drawing from them, that's likely your culprit.

Has it been parking outside overnight? Insulating the battery box makes a surprising difference. Mine improved noticeably once I sorted that.

Tommo55 | 234 posts

@Graham1995 Yeah this is completely normal mate. LiFePO4 does hold up well in cold as @EdMason says, but internal resistance increases as temperatures drop, which means the BMS can read lower apparent capacity because voltage sags more under load. You'll likely find your readings improve once the ambient temperature picks back up a bit.

Worth checking — is your Fogstar actually in the van overnight? If it's dropping below about 5°C regularly the chemistry just doesn't perform as efficiently. Some people stick a bit of insulation around their battery bank over winter which helps noticeably. Also make sure you're not charging it when it's below 0°C as LiFePO4 really doesn't like that — most decent BMS units will block it but worth being aware of.

Davo79 | 1,203 posts

@Graham1995 Worth adding to what the lads have said — the effect is more pronounced when the battery is actually cold at the time of use rather than just stored somewhere cold. If your van's been sitting overnight in near-freezing temps, the internal resistance shoots up, which is why your BMS readings can look odd. You're not necessarily losing permanent capacity, it's more that the battery can't deliver as efficiently when it's chilly.

Try running a load after the van's been warmed up a bit and see if the numbers improve. Also worth checking your charge settings — some chargers need a reduced charge current below around 5°C to avoid damaging the cells. Does your Fogstar have low-temp charge cutoff built in? Most of the Drift range does, but worth confirming.

24V_Queen | 1,203 posts

Worth quantifying what "lower" actually looks like here. A Fogstar Drift at 0°C will typically deliver around 80–85% of its rated capacity compared to 25°C — that's physics, not a fault. Where it gets interesting is internal resistance: cold cells show significantly elevated IR, which means your BMS voltage sag under load can trigger low-voltage cutoffs prematurely, making the capacity appear worse than it actually is.

What's your discharge rate and ambient temperature when you're seeing this? If you're pulling hard amps on a cold morning the sag will be brutal.

Also — critically for vans — never charge a LiFePO4 below 0°C unless your battery has a built-in low-temp cutoff (the Drift does, but worth confirming your BMS settings). Charging cold cells causes lithium plating which permanently degrades capacity. That could explain unusual readings if it's happened repeatedly.

SolarNotSure78 | 89 posts

Went through exactly this last January, parked up in Scotland for a fortnight in my motorhome. What caught me off guard wasn't just the reduced capacity — it was how suddenly the voltage would sag under load compared to summer. Kettle on, and the Victron BMV would momentarily show figures that looked genuinely alarming before settling back.

What helped me was pre-warming the battery compartment slightly before heavy loads — even just running the van engine for twenty minutes beforehand made a noticeable difference to how the Fogstar behaved.

@24V_Queen makes a good point about quantifying it. I'd add that the sag you see versus actual capacity loss are two separate things worth distinguishing — the BMS reading can look worse than reality during high-draw moments in cold conditions.

ShortCircuit56 | 847 posts

Good point from @24V_Queen on the numbers. One thing nobody's mentioned yet — if your van is sat unused overnight, the battery itself will be cold when you start drawing from it, which compounds what you're seeing. Even a small load like a diesel heater or some LED lighting for an hour or two will warm the cells slightly and you'll often see the apparent capacity creep back up mid-session. It's not the BMS lying to you, the cells are genuinely delivering less in that cold state. Worth checking whether your readings look worse first thing in the morning versus after you've had some draw on it for a bit. LiFePO4 is generally brilliant in cold compared to other chemistries but it's not immune, especially once you're dropping below 5°C consistently.

CliffWill | 312 posts

Interesting thread — I've got a Fogstar Drift in my motorhome too and noticed similar quirks last winter. One thing worth checking: are you doing full charge cycles regularly? I found my BMS was giving skewed capacity readings after weeks of only partial cycles. A proper full charge from low SOC seemed to recalibrate things noticeably. Also, where exactly is the battery sitting in the van? Mine's under the bed and temperatures there are surprisingly variable — even a few degrees makes a difference to what the Victron SmartShunt reports as available capacity.

FrankFisher | 203 posts

Worth noting that LiFePO4 handles cold better than other lithium chemistries, but it's not immune. The capacity reduction you're seeing is real — at around 0°C you can lose 15-20% of usable capacity, and it gets worse below that. More importantly, charging a cold LiFePO4 is the real concern. Most decent BMS units like the one in the Fogstar will throttle or block charging below about 5°C to protect the cells. So if you're plugging into hookup or running solar on a frosty morning, your battery may simply be refusing a full charge. What temperatures are you seeing overnight, @Graham1995?