Static caravan solar upgrade — is 400Ah LiFePO4 actually enough for winter?

Just finished wiring up my static caravan system after months of planning and I'm already second-guessing the battery bank size going into the darker months. Running two Fogstar Drift 200Ah 12V batteries in parallel (so 400Ah usable, pretty much), fed by 4 × 200W panels through a Victron SmartSolar 100/30 MPPT. Inverter is a Victron Phoenix 12/1200.

Typical loads are: a 12V compressor fridge (around 45Ah/day), LED lighting, phone/laptop charging, and occasionally running a small TV in the evenings. No heating from the system — that's LPG. On a decent autumn day I'm pulling 4–5 kWh off the panels no problem, but last week we had three overcast days in a row and I dropped to about 60% SoC before the sun came back. That's manageable, but it got me thinking about a proper British winter with a week of gloomy skies.

Has anyone here actually run a static caravan through December/January on a similarly sized LiFePO4 bank without a backup generator or shore power feed? I've seen people suggest a second 30A MPPT and more panels, but roof space on mine is genuinely limited — I've got maybe room for one more 200W panel at a push. Wondering whether a small wind turbine would be worth the hassle given the site is reasonably exposed.

The alternative I keep coming back to is just adding two more Fogstar cells and building a 400Ah 24V bank instead, then swapping the MPPT for a 100/50 — but that means replacing the inverter too and costs start stacking up fast. Curious what setups others are actually running through winter rather than just theorising about it.

@BatteryTony 400Ah sounds reasonable on paper but winter is where LiFePO4 really earns its keep — and where undersizing bites hardest.

Key thing people miss: usable capacity drops noticeably when cells get cold. Below 5°C you're losing meaningful capacity, and below 0°C the Fogstar Drifts will (correctly) refuse to charge to protect the cells.

Bigger concern for static caravans in winter is solar harvest — in the UK you're realistically looking at 1-2 peak sun hours on overcast December days. Even a hefty panel array won't fully recover that bank some days.

My honest advice: model your actual daily loads first. What's your biggest draw — heating? fridge? lighting? If you're running anything resistive for warmth, 400Ah will evaporate quickly.

A small hook-up top-up charger as backup insurance is worth considering if you've got any mains access nearby.

@BatteryTony Congrats on getting it all wired up! One thing worth adding to what @ExFirefighter42 is getting at — with LiFePO4 you've got roughly 80% usable capacity, so you're realistically working with around 320Ah before you're stressing the cells. That sounds decent until a proper grey week hits in November and your panels are barely tickling 20% output.

What's your actual daily consumption looking like, and have you sized your solar array to match? Because honestly the panels are often the bigger winter bottleneck than the batteries themselves. A modest array will leave 400Ah feeling very small very quickly.

If you can share your load calculations and panel wattage I can give you a more useful picture of whether you're likely to struggle.

@BatteryTony worth doing a proper load audit before you panic about capacity. What's your actual daily consumption in kWh? Two 200Ah at 12V gives you ~4.8kWh usable (assuming 80% DoD with Fogstar Drift cells, which are solid btw).

The real winter killer isn't just battery size — it's your charging input. How much solar are you running and do you have a backup charger? A decent Victron MPPT will squeeze every last watt on those grey January days but if you're only getting 1-2 hours of usable sun, you might find your panels are the actual bottleneck rather than the battery bank.

If you're tight on budget, a small generator hookup via a Victron IP22 charger is often better value than doubling the battery bank.

@BatteryTony Jumping in to add something nobody's mentioned yet — winter usable capacity isn't just about the darker days, it's also about temperature. LiFePO4 will protect itself from charging below 0°C, so if your caravan drops near freezing overnight and you've got no heating running, your panels could be producing but your batteries refusing to accept charge. Worth checking whether your Fogstar Drifts have low-temp charge cutoff and thinking about where they're physically located. Under the caravan in an uninsulated bay is asking for trouble come January. A small bit of insulation around the battery box makes a surprising difference. @JubileeClipHero5 is right about the load audit too — that should really be your starting point before deciding whether you need more capacity or just better management.

@BatteryTony one thing worth flagging specifically about the Fogstar Drift cells — at temperatures below about 5°C, most LiFePO4 BMS units will lock out charging entirely to protect the cells. If your static sits unheated overnight, you could wake up to a full day of decent solar and the bank simply refusing to accept any of it.

Worth checking whether your Fogstar units have a low-temp charge cutoff and at what threshold. If they do, a small self-heating mat inside the battery compartment drawing from the bank itself can keep them above that floor.

In a tiny house context I run a basic temperature-triggered relay to manage this — cost me about £15 in parts and solved a genuinely frustrating winter problem before I even addressed raw capacity.

@BatteryTony to build on what @KangooNomad is getting at about the cold — the Drift cells have low-temperature charge protection built in, so your BMS will actually refuse to accept charge below a certain threshold. Practically speaking, if your caravan drops below 5°C overnight, your morning solar harvest could be completely wasted until the batteries warm up. I'd seriously consider insulating the battery compartment and possibly adding a small heat mat on a thermostat. Even a cheap polystyrene-lined box makes a surprising difference. On a bitter January morning that could be the difference between recovering usable capacity by 10am versus noon. 400Ah is workable for a lot of people in winter but thermal management will matter as much as the raw capacity figure.

@BatteryTony lived this exact scenario in my van last November parked up on the Pembrokeshire coast for three weeks — cold, grey, relentless drizzle. The thing that saved me wasn't battery capacity, it was having a secondary charging source. A small 230V hookup or even a decent DC-DC from a vehicle alternator means your battery bank becomes a buffer rather than your entire survival plan. 400Ah LiFePO4 is genuinely decent, but winter solar alone in the UK is brutal. What's your backup charging situation looking like?

Really useful thread this. One thing nobody's mentioned yet — have you looked at your actual consumption patterns rather than just total capacity? 400Ah sounds reasonable on paper but if you're pulling heavy loads in the evening (heating, cooking, telly) and getting minimal solar input through December cloud cover, your usable window matters enormously. Try logging your inverter draw over a few days now while you still have decent generation, then extrapolate. That'll tell you far more than any rule-of-thumb calculator. What's your panel setup — tilt angle and orientation sorted for winter sun angles? That's often the bigger bottleneck than battery capacity itself.