How many batteries for a weekend cabin?

Right, trying to sort out the battery situation for a weekend bolt-hole in the Cotswolds and I'm thoroughly befuddled by the maths.

Currently running a modest 400W solar array with a Victron MPPT controller, and I'm thinking about adding storage since relying on the grid's umbilical cord defeats the purpose entirely. The cabin's got a gas cooker, woodburner for heating, but the essentials are fridge, lighting, water pump, and enough juice to charge devices without feeling like I'm rationing leccy like it's 1940s.

Usage pattern's probably 5-6 kWh per weekend in winter (darker, longer evenings), maybe 3 kWh in summer when there's daylight to spare. Nothing mad, but I'm not roughing it either.

Here's my confusion: everyone online seems to either have 10 kWh of batteries or a Honda generator propping up their setup. Is there a sensible middle ground? I've been eyeing a Fogstar 5.12 kWh unit as a starter, but honestly can't figure out whether that's overkill for weekend usage or whether I'll be cursing myself come February when the sun decides to have a prolonged nap.

Should I start smaller and expand, or bite the bullet and get something decent that'll last the distance? And before anyone asks—no generator, didn't survive this long avoiding them to cave now.

What's everyone actually using for part-time off-grid that isn't bonkers expensive?

Mate, 400W solar on a weekend cabin is like bringing a flask to a festival — technically fine if you're modest with the tea.

Real talk though: what're you actually running? Fridge, heating, lights? That's the missing bit. If it's just occasional kettle and some LED strips, a couple of LiFePO₄

Depends entirely on your usage pattern though, doesn't it? Weekend cabin is the key bit here.

Are you charging devices, running lighting, maybe a fridge? If it's just occasional use—say, Friday evening through Sunday—a decent 10-15kWh lithium bank would give you a comfortable buffer even with poor weather. Keeps your charge cycles reasonable too.

The real question is: how much are you actually drawing? I've got a similar setup in my motorhome and found I was way overestimating consumption. Once I logged actual usage for a month, I realised I could comfortably run on half what I'd planned.

Have you metered what a typical weekend looks like? That'll tell you whether 400W solar needs backing with 5kWh or 20kWh of storage. Also worth factoring in—do you need to come home Sunday fully charged, or can you taper usage as the weekend progresses?

@OldSailor the real question is whether you're actually at the cabin or just thinking about being at the cabin (I've got three mates with weekend places they visit twice a year, mate).

400W will happily charge phones and run lights. For anything beyond that — heating water, powering a kettle, running a mini fridge — you're going

@OldSailor — the real limiter is whether you're there weekends only or doing longer stints. I learned this the hard way with my narrowboat setup.

400W solar is decent, but winter weekends in the Cotswolds? You're looking at maybe 800Wh actual generation on a grey day. Add in heating, cooking, and phone charging, you'll drain a 5kWh battery bank in a night.

Go for 10kWh lithium minimum if you want proper comfort — that gives you a 3-4 day buffer without panicking about cloud cover. A Victron 48/5000 with two 5kWh LiFePO₄ stacks (Fogstar or similar) will handle your 400W array fine. The MPPT controller you've got is solid.

Skip oversizing the battery if you're genuinely just weekends — but don't go under 8kWh either. I've seen too many folks add more solar only to realise they needed capacity, not generation.

What's your actual weekend consumption look like? Heating included?

@OldSailor — the 400W array is workable but you're right to think through battery sizing carefully. The real crux is your discharge window over a weekend.

Let's say you're there Friday evening through Sunday afternoon (roughly 60 hours). If you're consuming 1kWh daily for basics (lighting, heating, fridge), that's 2.5kWh over the weekend. You'll also need headroom for cloudy days — I'd add 50% as a minimum buffer, which puts you at needing 4kWh usable capacity.

A single 5kWh LiFePO₄ unit (Victron LiFePO₄ Smart or similar) gives you decent cycling depth without accelerating degradation. If budget's tight, two 2.56kWh units work identically and offer redundancy.

The 400W array should recharge that comfortably mid-week if you're returning to grid power, but if the cabin sits idle during the week, you'll need to size for seasonal winter generation — which gets grim in UK latitudes.

What's your actual usage profile? Heating or just auxiliary loads? That'll reshape the recommendation entirely.

Depends on loads really. 400W is tight for winter weekends — you'll struggle to generate much Nov-Feb.

Start by actually logging what you use over a weekend. Fridge, lighting, heating? That's your baseline. Then work backwards: if you're pulling 2kWh/day and have maybe 10 peak sun hours across a weekend in decent weather, your 400W array gives you ~2kWh generation if conditions cooperate.

I'd say minimum 10kWh usable capacity for genuine autonomy, more like 15kWh if you want headroom and don't want to babysit consumption. Lithium makes sense for cabin use — better depth of cycle and you're not regularly draining/charging like a daily-driver setup.

@BoxerCamper's right about usage patterns being the real decider. One weekend a month is totally different from every other weekend.

What's your heating situation? That's usually the killer load nobody budgets for properly.

@OldSailor — winter's your constraint here, not summer. With 400W you're looking at maybe 800–1200Wh realistic generation on a decent December day in the Cotswolds, less if it's cloudy.

What loads are we talking? That makes all the difference. If you're running heating, forget it — you'll need either mains backup or accept cold weekends. But if it's just lights, fridge, and the occasional kettle, you can get away with less.

I'd suggest starting with 10kWh usable (so ~12–13kWh nominal LiFePO4). That gives you a 3-day buffer without sun, which is realistic for winter. You could go smaller — 5kWh — but then you're relying on either having decent weather or topping up from the grid.

The Victron kit you've got is solid. Pair it with a decent inverter and you're golden. Just don't skimp on the battery itself. A cheap cell will haunt you for years.

@OldSailor — what are your actual loads? That's the missing piece here.

I'm running a static caravan setup with similar solar, and it makes a massive difference whether you're talking fridge, heating, or just lights and a kettle.

Winter generation is grim with 400W — @DODQueen's spot on there. I'd aim for 10–15kWh usable capacity minimum if you want proper autonomy Nov–Feb without babysitting the system. That's probably 2–3x LiFePO4 batteries depending on your DoD comfort level.

Alternatively, size for summer self-sufficiency and accept you'll need hookup or a backup gen in winter. Honestly? If it's just occasional weekends, a smaller bank (5–8kWh) + petrol gen is cheaper than buying your way out of winter shortfalls with batteries.

What's your typical weekend draw look like?

@OldSailor — you're going to need specifics on your actual consumption to answer this properly. The 400W array is your constraint in winter, agreed with @MarineGaz, but storage depends entirely on what you're running.

I've got a shepherds hut setup with 2kWh usable (Victron LiFePO4) paired with 800W panels, and even that feels tight November through January if you've got heating or a decent fridge running continuously. Weekend cabin usage is different though — you're not drawing 24/7.

Work backwards: list your loads (heating, lighting, fridge, water pump, whatever), multiply by estimated daily hours, then add 20% buffer. That's your daily requirement. For weekends with overcast weather, I'd typically spec 3–5 days autonomy minimum.

Given your 400W setup, I'd be looking at 2.4–3kWh usable LiFePO4 minimum to avoid dropping below 20% state of charge regularly. Cheaper lead-acid would need proportionally more capacity.

What's actually drawing power at the

@OldSailor — I've been down this exact road with my cabin setup. The real answer depends on what "weekend" means to you. Are you there Friday to Sunday with heating, or just popping in for a brew and a walk?

I started with too small a battery bank and it was painful. My 400W array paired with a 10kWh LiFePO₄ gives me genuine peace of mind November through March. Without that capacity, you're constantly rationing.

The winter generation @DODQueen mentioned is spot on — I get maybe 60–70% of summer output on a grey December afternoon. With only 400W and a modest load, you might squeeze by with 5–6kWh, but you'll be watching your SOC like a hawk and limiting kettle use.

What's your heating situation? That's usually where weekend cabins either work brilliantly or become a false economy. If you're running a Webasto or air-source heat pump, you need substantially more storage.

What loads are we actually talking about?

Fair point from @ZFS_OffGrid and @LesWood78 — you need to nail down your actual consumption first. Winter weekends are brutal; summer ones are manageable with less storage.

What I'd do: Spend a weekend monitoring everything. Lights, heating, fridge, kettle — log it all. That'll tell you if you're looking at 5kWh or 20kWh per day.

400W solar is your constraint, not your friend in November. On a decent summer day you might get 1.5-2kWh; in winter, maybe 0.3kWh. That's a massive swing.

For a rough starting point: if you're heating with gas and running basic 12V lighting, a pair of 5kWh LiFePO4 banks (10kWh usable) gets you through most weekends. If you're all-electric, you're looking at 20kWh+.

I've got three Fogstar 5.12kWh modules in my motorhome — overkill for weekends but I use it constantly. Worth the

You lot are right about the consumption audit being essential, but I'll add something practical from my narrowboat setup—400W is genuinely tight for winter weekends, especially in the Cotswolds where you're looking at maybe 1-2 peak sun hours December-February.

Here's what I'd actually do: assume you'll generate roughly 1kWh per day average over the year (site-dependent), then halve that for winter. If you're pulling 2kWh over a weekend, you need enough battery to cover the shortfall between what solar generates and what you consume.

The LiFePO₄ route—Fogstar, Victron LiFePO₄ Smart, or similar—gives you better usable capacity than lead-acid. A 5kWh LiFePO₄ bank lets you actually use 4.5-5kWh reliably without stuffing the chemistry. Lead-acid equivalent would need 10-12kWh nominal.

What actually matters: daily consumption breakdown (heating/hot water/lighting/gadgets?), and whether you're buffering against cloudy weekends or just typical use. Winter vs summer changes everything.

Post your actual load profile and I can ballpark a sensible battery size without guesswork.

The consumption audit is absolutely crucial, but here's what I'd add from my shepherd's hut experience: don't just estimate based on what you think you'll use. Actually measure it for a weekend or two.

I reckoned I'd need 10kWh per weekend. Reality? Closer to 6kWh in summer, 14kWh in winter once heating kicked in. The difference was massive.

With your 400W array, you're looking at maybe 1.2–1.5kWh per day in decent conditions (less in winter). So you need enough battery to cover the shortfall between generation and consumption.

My honest take: aim for 3–5 days' autonomy minimum. That means if you're genuinely using 2kWh per day, you want 6–10kWh usable capacity. A pair of Fogstar or Victron LiFePO₄ batteries would handle that nicely without breaking the bank.

The other thing — make sure your MPPT controller is actually sized properly. A 400W array with a smaller Victron 75/15 will throttle

Right, 400W with a Victron MPPT means you're onto it—but winter in the Cotswolds is brutal for solar. I'd reckon 10-15kWh usable storage minimum if you're not wanting candlelit dinners by 4pm. Lithium or LiFePO₄? That'll shift your sums considerably.