Anyone else finding their lithium bank struggles in cold UK winters?

Running a 200Ah Fogstar Drift LiFePO4 on my narrowboat and noticed a significant drop in usable capacity once temps dropped below about 5°C this past December. Wasn't expecting it to be quite so dramatic — I reckon I was only pulling maybe 140Ah before the BMS started grumbling.

I've got a Victron SmartShunt keeping an eye on things, so the data's pretty solid. The Drift doesn't have built-in heating, which I suspect is part of the problem. Has anyone added an external battery heating pad to a bare LiFePO4 bank, and did it actually make a meaningful difference or is it more faff than it's worth?

Also wondering whether the charge voltage needs adjusting in winter — my Victron MPPT is set to 14.2V absorption, same as summer. Should I be bumping that up slightly when it's cold, or does that risk doing damage?

@ForestDweller oh mate, the cold temperature derating on LiFePO4 is absolutely real and catches everyone out the first winter!

The chemistry genuinely loses usable capacity as temps drop — you're looking at roughly 80% capacity around 0°C and it nosedives further below that. Fogstar's own spec sheets acknowledge this.

The bigger concern though: never charge below 0°C or you'll plate lithium dendrites onto the anode permanently — nasty irreversible damage. Your BMS should cut charging, but worth verifying it actually does at that threshold.

My fix on my tiny house setup: I insulated the battery compartment and added a small Victron temperature-compensated charge profile. The thermal mass of a narrowboat hull actually helps somewhat, but mooring somewhere particularly exposed will hammer you.

Worth checking whether your Fogstar Drift BMS has low-temp charge cutoff enabled — not all come pre-configured for it out the box!

Yeah, @ForestDweller, this caught me out badly my first winter too. Worth noting it's not just capacity loss you need to watch - charging below 0°C can actually cause permanent lithium plating on the cells, so if you haven't already, make sure your BMS has low-temperature charge cutoff enabled or you could be doing lasting damage rather than just temporary derating.

On the narrowboat specifically, have you considered insulating the battery compartment? I've got mine wrapped in rigid PIR board in my Berlingo and it holds heat surprisingly well overnight just from residual warmth. On a boat you've presumably got a stove running, so you might be able to route some gentle warmth that way. The Fogstar Drifts are decent cells, they'll perform fine once you've sorted the thermal management. Don't panic yet!

Really feel this one, @ForestDweller. Worth adding that the BMS will also cut charging if cell temps drop too low - typically around 0°C for most LiFePO4 systems. So you can end up in a frustrating situation where your solar or alternator is producing perfectly well but the battery simply refuses to accept charge. On a narrowboat you've at least got the option of running the engine regularly which generates some warmth, but I'd seriously look into a self-heating battery for your next upgrade, or even just wrapping the existing bank in some decent insulation to retain whatever ambient heat is around. The Fogstar Drift is a solid unit but none of them are immune to the physics unfortunately!

@ForestDweller living this nightmare on my own boat — BMS said "nope" on a -3°C morning last January and left me with a very cold and very dark breakfast situation that no amount of emergency backup planning had prepared me for.

@ForestDweller — something worth adding that nobody's mentioned yet: even when your BMS does allow charging in the cold, you're potentially causing lithium plating on the anode cells if you're pushing any real current through them below around 5°C. Long-term it degrades capacity permanently rather than just temporarily.

Practical fix I've used on my own setup — a small self-regulating heat mat wrapped around the battery, wired to come on via a simple thermostat probe set to kick in around 5°C. Draws minimal power overnight and keeps everything happy. Fogstar Drifts are decent cells so worth protecting properly.

Also worth checking whether your charger has a dedicated low-temp compensation setting — some Sterling and Victron kit has this built in and will taper charge current automatically. Saves a lot of faff.

Adding to what @LazySparky was getting at — the reduced charge acceptance in the cold isn't just a capacity issue, it's worth watching your actual charge rate carefully. Even if the BMS permits charging, pushing lithium hard at low temps can cause lithium plating on the anode, which permanently degrades your cells over time. Not something you'd notice immediately but it accumulates.

On the narrowboat specifically, if you've got any engine runtime during cruising, your alternator could be hammering away at those cold cells without you realising. A DC-DC charger with a proper temperature sensor will throttle back accordingly rather than just blindly chucking amps in.

Worth checking whether the Fogstar Drift has a temperature sensor on the BMS output — some budget packs do, some don't. If yours doesn't, an external battery temperature monitor is cheap insurance.