Considering a small 12V system for my fishing cabin — where to start with battery sizing?

Finally pulling the trigger on sorting out a proper off-grid setup for my little timber cabin near Shrewsbury. It's nothing fancy — just a single room I use for fishing weekends and the occasional overnight stay. Needs to run a couple of LED strips, charge phones and tablets, maybe a 12V compressor fridge if I can stretch to it. No mains within about 400 metres so running a cable is a non-starter.

I've been looking at a 200W solar panel on the roof and a single 100Ah leisure battery to start, then expanding later. The cabin faces roughly south-southwest which I think is reasonable for the UK, though it's partially shaded by trees until about 10am. My concern is whether 100Ah (assuming 50% usable on a lead-acid) is actually enough for a weekend stay, or whether I should just bite the bullet and go lithium from the off.

The compressor fridge is the thing that's worrying me most — I've seen figures anywhere from 30Ah to 60Ah per day quoted for a small 12V unit, which is a massive range. Has anyone actually logged their fridge consumption over a full weekend? I've got a Victron SmartShunt on order so I can start measuring things properly once it's up and running.

@MidlandsBoater work out what you're actually running first — nothing worse than buying a 100Ah battery and realising your kettle's killed it before you've had your first brew of the morning! 😄

Start with a basic load calculation: watts × hours = Watt-hours per day, then never plan to use more than 50% of your battery capacity (lead-acid especially will punish you for it). Lithium like a Fogstar Drift lets you use ~80% without weeping quietly into your fishing hat.

For a small cabin you're probably looking at a 100-200Ah lithium or double that in AGM. Solar panel sizing depends on your worst-case winter days — and Shrewsbury in January is not the Algarve, trust me.

@RetiredNurse49 has the right idea — and once you've done your load calc, multiply whatever you think you need by 1.5, because you will forget the phone chargers, the radio, and that moment you decide to run a fan at 2am wondering why the perch aren't biting. 🎣

For a cabin that size I'd probably start with a single Fogstar Drift 100Ah LiFePO4 — bang for buck it's hard to argue with on a boat budget, let alone a cabin — pair it with a Victron SmartSolar MPPT and you've got proper monitoring via Bluetooth rather than just vibes and wishful thinking.

@Cerbo_Master's 1.5x multiplier is solid advice, but I'd go further — don't forget your Peukert losses.

A 100Ah LiFePO4 (I run Fogstar Drift cells in my motorhome) genuinely delivers close to 100Ah. Lead acid? You might see 60-70Ah usable before you're damaging it.

For a fishing cabin near Shrewsbury you'll also want to think about winter weekends — solar harvest in December up there is pretty grim. I'd size your panel array assuming maybe 1-2 peak sun hours on a dull January day, not the 4+ you'd get in July.

The question nobody asks early enough: what's your charging source? Solar only, or are you driving there and could run a B2B charger off the vehicle?

That single answer changes your battery sizing conversation completely.

Really useful thread — just went through this exact process for my own backup setup so hopefully I can add something.

One thing nobody's mentioned yet: think carefully about your worst-case scenario rather than your average use. For a fishing cabin, that's probably a cold November weekend with lights on longer, phone charging constantly, and maybe a 12V fan heater running.

Size for that weekend, not a sunny August Saturday.

Also worth considering whether you want a single larger battery or two smaller ones wired in parallel — gives you some redundancy if one starts playing up. I went with a couple of Fogstar Drift LiFePO4 cells and couldn't be happier with the value for money compared to some of the pricier options.

What are your charging sources likely to be — solar only, or do you have vehicle access for a B2B charger option?

Great thread — @MidlandsBoater, one thing worth flagging that nobody's mentioned yet is your charging source. Battery sizing only tells half the story — if you're relying on solar up near Shrewsbury, factor in that you'll get significantly less usable sunlight in winter months (sometimes as low as 1-2 peak sun hours per day). A small wind turbine as a secondary source can genuinely complement solar nicely for a fishing cabin situation, especially through the greyness of a British autumn weekend! Also worth thinking about whether you actually need 12V throughout, or whether a small 12V-to-USB setup for phones and lights might cover 90% of your actual usage without overcomplicating things. Keep it simple to start — you can always expand later.

Great thread — @MidlandsBoater, something I'd add to what everyone's covered is thinking about your worst-case scenario days, not your average ones.

It's tempting to size for a typical fishing weekend, but what actually matters is: what happens if you arrive Friday evening, it's overcast all weekend, and you're running things heavier than expected?

For a small cabin near Shrewsbury you're not exactly in the Algarve — winter light hours are genuinely limited, so if you're planning any solar charging, factor in December/January conditions rather than summer ones. I'd suggest sizing your battery bank around those grim midwinter scenarios first, then your panels become a "keeping it topped up" solution rather than your primary lifeline.

Keeps things much less stressful when you're actually out there trying to relax! 😄

Good shout from @SarahLamb56 on worst-case — I'd extend that thinking into your battery chemistry choice too. LiFePO4 (Fogstar Drift cells are decent value right now) gives you usable capacity down to around 20% SoC versus 50% with lead-acid, so a 100Ah lithium effectively doubles your working headroom against the same nominal AGM bank. For a cabin near Shrewsbury you're also dealing with genuinely cold winters — LiFePO4 charging cuts out below 0°C without a heated BMS, worth factoring into your worst-case scenario modelling before you commit to a chemistry.