Does battery capacity drop noticeably in winter? Seeing weird numbers on my 100Ah LiFePO4

So I've got a 100Ah LiFePO4 (Fogstar Drift) in my Transit camper and I'm noticing it's behaving oddly now the temperatures have dropped. Last night it got down to about 4°C inside the van and this morning my Victron BMV-712 was showing what looked like a much lower usable capacity than usual. Normally I can run my 12V compressor fridge and a few USB charges through the night without much drama, but lately it's hitting low voltage warnings earlier than expected.

I know LiFePO4 is supposed to handle cold better than other lithium chemistries, but I'm starting to wonder if there's still a meaningful capacity drop happening in the 0–10°C range. I've read conflicting things — some sources say you lose maybe 10–15% below 10°C, others seem to suggest it's more dramatic than that. Has anyone actually tested this properly or noticed it in real-world use?

Also worth mentioning — I'm not trying to charge it when it's that cold, I've got low-temp cutoff set on my Renogy DC-DC charger so that side should be fine. This is purely about discharge performance. Is what I'm seeing normal, or should I be looking at whether something else is going on with the battery or the BMV calibration?

@Ollie1991 here's what's actually happening under the hood: LiFePO4 internal resistance climbs significantly as temperature drops, which means the BMS reads voltage sag under load and interprets it as lower state-of-charge than reality. At 4°C you're probably looking at 10-15% usable capacity reduction compared to 25°C baseline — nothing catastrophic, but noticeable.

The Fogstar Drift's BMS will also throttle charge acceptance below 5°C to protect the cells from lithium plating during charging. So if your solar or alternator is pushing amps into a cold battery at dawn, it may be quietly limiting current without telling you.

Worth checking: is your Victron (or whatever shunt you're using) showing genuine Ah throughput, or just voltage-based estimation? Voltage-based readings go completely haywire in the cold.

Insulating the battery compartment made a measurable difference on my own setup.

Hey @Ollie1991, to add to what @TorJake is saying - the usable capacity reduction you're seeing is real and expected, but the good news is it's not permanent damage. Once the cells warm back up you'll get your full capacity back.

One practical tip: if you're running a heater overnight anyway, try positioning it so some warmth reaches the battery compartment. Even getting it up to 10-15°C makes a noticeable difference to performance.

Also worth checking - is your BMS cutting off charging at low temps? The Fogstar Drift should have low-temperature charge protection built in, which means it'll refuse a charge below around 0°C to protect the cells. That can sometimes look like odd behaviour if you're not expecting it. What are your morning readings showing on the battery display?

Interesting thread — I've been wondering about this too for my garden office setup.

Quick question for @TorJake and @BKU_Electric: does the low-temperature cutoff on the BMS kick in before you'd even notice the capacity drop, or are these two separate things to worry about?

My concern is whether I should be looking at a heated battery enclosure rather than just oversizing capacity. Has anyone actually tried something like a small insulated box with a thermostat-controlled heat mat? Seems like it could be more cost-effective than buying extra cells.

Also wondering — does the Victron BMV-712 report actual usable capacity at low temps, or does it still show numbers based on the rated 100Ah? If it's calculating SoC incorrectly that might explain the weird readings @Ollie1991 is seeing?

Great thread this. One thing worth adding that hasn't been mentioned yet — if you're charging at those low temps, do make sure your charger/BMS is set up properly. LiFePO4 really doesn't like being charged below about 5°C, and some cheaper BMS units won't cut out fast enough to protect the cells. The Fogstar Drift does have low-temp charge protection built in IIRC, but worth double-checking yours is actually triggering correctly @Ollie1991.

Also for @Liz1979 with the garden office — a static setup might actually benefit from a small self-heating battery or just some basic insulation around the battery box through winter. Makes a surprising difference.

Really useful thread this. Just to add to what @T6Adventure mentioned about charging — worth knowing that LiFePO4 actually handles cold temps better than most other lithium chemistries, so you've made a good choice with the Drift.

The capacity loss you're seeing is temporary though, @Ollie1991 — once the cells warm up through use (or if you can insulate the battery a bit), you'll get your numbers back to normal. A simple piece of closed-cell foam around it makes a surprising difference in a van environment. Some folk even route a bit of warm air from the cab heating past the battery box overnight. Nothing fancy needed really.