Shepherd's hut battery sizing — am I massively overthinking this?

Been planning my shepherd's hut build for about 18 months now and I keep going round in circles on the battery bank. Currently leaning towards 2x Fogstar Drift 12V 200Ah in a 24V config, which gives me around 4kWh usable (at the 80% LFP figure). Hut will have LED lighting, a small 12V fridge, phone/laptop charging, and maybe a 300W inverter for occasional power tools.

I've done the load calc multiple times and my worst-case daily usage comes out at roughly 1.2–1.5kWh. So 4kWh gives me 2–3 days of autonomy before I'd need to think about solar input. That sounds fine, but part of me keeps eyeing up going to 4x cells for a proper 400Ah bank "just in case."

The hut is also going to be my occasional WFH spot, so there's a laptop running 6–8 hours some days, which bumps the numbers up. No EV charging from this system — that's a separate project — but I want headroom without massively oversizing and spending money I don't need to.

Has anyone actually run a similar setup in a shepherd's hut or small cabin and found 4kWh was plenty, or did you end up wishing you'd gone bigger from day one?

@NeilBurns91 what's your actual daily load looking like? That's the bit that always gets skipped over before people jump to capacity figures.

I went through exactly the same loop before my own build — kept fixating on the bank size without properly auditing what I was actually running. Ended up with a spreadsheet listing every load, hours per day, and whether it was summer or winter use.

The Fogstar Drift is a solid choice for the money, but 400Ah usable at 24V might be overkill or undersized depending on whether you're heating anything, running a compressor fridge, that sort of thing.

What's your solar array sitting at, and is this year-round use or mostly spring/summer? Winter in the UK completely changes the equation — those short grey days kill a lot of "should be fine" assumptions.

@NeilBurns91 Honestly that Fogstar setup sounds pretty reasonable for a shepherd's hut — they're cracking batteries for the money. But yeah, @George1972 is right, loads are everything here.

One thing worth considering though: are you planning to use it year-round? Winter usable capacity from solar drops off a cliff in the UK and you'll be drawing more for lighting. A lot of people size for summer and then wonder why they're struggling in November.

Also, 24V is a solid call over 12V at that capacity — keeps your cable losses and wire gauges more manageable in a small space.

What solar array are you pairing with it? That's often where the real bottleneck ends up being, not the batteries themselves.