Anyone else finding their lithium setup struggles in the cold this winter?

Noticed something a bit frustrating over the last few weeks — my 200Ah LiFePO4 bank (a pair of Fogstar Drift 100Ah in parallel) has been noticeably grumpier since temperatures dropped. Woke up to -3°C last Tuesday and the BMS had tripped overnight, left me with nothing for the morning. Charged fine once things warmed up past about 5°C, but it's not ideal when you're relying on it day-to-day.

I've got a 400W solar array on the roof feeding into a Victron MPPT 100/30, and I've read the controller will back off or refuse to charge below freezing to protect the cells — which is fair enough, but it caught me off guard. Thinking about adding a small heating mat under the battery box, something like the ones people use for reptile tanks, run off a timer or a thermostat. Has anyone actually done this, or is there a better way to handle it?

Also curious whether anyone's noticed capacity drop-off in the cold even when the BMS doesn't trip. Mine feels like it's giving maybe 70-75% of its usual usable capacity on cold mornings before it recovers. Is that just normal LiFePO4 behaviour or should I be looking at something else?

Yeah @BurnKen, LiFePO4 definitely sulks below about 5°C — you'll lose a noticeable chunk of usable capacity and the cells just don't deliver current as freely. The Fogstar Drifts are decent batteries but they're not doing anything magical against physics unfortunately.

Worth checking whether your BMS is cutting charge acceptance at low temps — most decent ones will, which is actually protecting you rather than misbehaving. Charging a cold lithium cell can cause lithium plating which permanently damages capacity.

If the batteries are somewhere uninsulated, even wrapping them loosely with some closed-cell foam makes a surprising difference overnight. Some folks use a small self-regulating heat mat on a thermostat, powered from a small lead-acid buffer — bit of a faff but solves it properly.

What's your overnight low inside the van/shed/wherever they're sitting?

@BurnKen the cold performance drop is well documented with LiFePO4 — internal resistance climbs significantly below 5°C, so you'll see both reduced usable capacity and the BMS cutting charge acceptance to protect the cells.

Worth noting: the Fogstar Drift BMS typically locks out charging below 0°C, which is the right call — charging cold lithium causes lithium plating on the anode, permanently degrading the cells.

A few practical options:

• Self-heating batteries (Fogstar do a heated variant) use a small discharge current to warm cells before charging kicks in
• Insulating your battery enclosure makes a surprisingly big difference — I use 25mm Celotex in my van build
• Route your alternator charge through a DC-DC charger (Victron Orion-Tr Smart) which you can programme with temperature cutoffs

What's your current charge source — solar, alternator, or mains?

Yeah, @BurnKen, something worth checking if you haven't already — most decent BMS units will actually cut off charging entirely below 0°C to protect the cells from lithium plating, which can cause permanent damage. So if your panels are producing but nothing's going in, that's likely why rather than a fault.

One practical fix I've seen work well is a small self-regulating heat mat underneath the batteries, triggered by a thermostat set around 5°C. Doesn't draw much overnight and keeps things in the happy zone. @LazyMechanic and @PartnerAdventure are right about the performance drop, but the charging restriction is arguably the bigger headache in practice — you can still discharge fairly happily even when it's cold, just don't expect full capacity.

How's your battery enclosure set up? Insulating the box itself makes a surprising difference even without active heating.

Good shout from @LesKnight on the BMS charge cutoff — that's caught a few people out. One thing nobody's mentioned yet though: even if your BMS allows charging in the cold, your actual charge acceptance will be pretty poor and you risk damaging the cells long-term. Worth looking at whether you can add a small self-regulating heating pad directly to the battery — they draw very little and can keep the bank above that critical threshold overnight. Some people rig theirs to a simple thermostat controller so it only kicks in below 5°C. Alternatively, if your setup allows it, simply insulating the battery compartment better can make a surprising difference without any added complexity. How's your battery situated, @BurnKen — inside a vehicle, shed, or fully exposed?

Great points from everyone already. One thing I'd add @BurnKen is to look at self-heating battery options if you're planning to expand or upgrade down the line — some of the newer LiFePO4 cells have built-in heating pads that kick in before charging begins. Fogstar actually do a heated version of the Drift now I believe.

In the meantime, even just wrapping your existing bank in some decent insulation (camping mat foam works a treat) can help retain overnight warmth if they've been charging during the day. Won't solve the problem entirely but it slows the temperature drop considerably.

Also worth checking your actual resting voltage in the morning before any loads kick in — that'll give you a clearer picture of whether you're losing capacity or just suffering from high internal resistance temporarily. The two behave quite differently once temps recover. 👍