Anyone know if a 200Ah lithium battery is overkill for a small shepherd's hut?

Been mulling this over for a while and thought I'd ask here before pulling the trigger on anything.

I've got a small shepherd's hut — about 14ft — that I want to set up with basic off-grid power. We're talking a few LED lights, a 12V fan, charging phones/laptops, and maybe a small 12V compressor fridge at some point. Nothing wild.

I've been looking at the Fogstar Drift 200Ah as it seems decent value, but I'm genuinely not sure if that's oversized for what I need. My narrowboat runs a 200Ah setup and that feels right for that lifestyle, but the hut is far more occasional — weekend use mostly, sometimes a week in summer.

A few questions if anyone has thoughts:

• Would a 100Ah be sufficient for the fridge + lighting load, or does the fridge push you toward 200Ah pretty quickly?
• Is there a meaningful cost-to-capacity sweet spot I'm missing?
• I'd also want this to double as emergency backup at home if needed — does that change the calculus at all?

I know the usual answer is "more capacity is always better" but I'm trying to be realistic about budget. Don't want to overspec when a smaller bank would genuinely do the job — equally don't want to regret going small the first time the fridge runs overnight and I wake up to a low voltage alarm.

Anyone running a similar small setup who can share actual real-world numbers?

@BordersOffGrid ooh, the eternal question — "is this too much battery?" (Spoiler: almost never.)

I spent weeks agonising over sizing for Doris (my van), convinced I was going overboard with 200Ah. Turns out I was underboard once I added a small fan, phone charging, lights, and — crucially — a laptop for "just a bit of work."

A shepherd's hut is similar vibes. 200Ah lithium (Fogstar do cracking value cells) actually only gives you 100Ah usable in practice once you factor in sensible discharge habits. That evaporates faster than you'd think on a grey British week with minimal solar input.

What's your solar situation? That matters as much as the battery. A beefy bank paired with a stingy panel is just an expensive paperweight waiting to happen. 🌧️

@BordersOffGrid running a 14ft hut myself and honestly 200Ah is pretty much the sweet spot. I've got a Fogstar Drift 200Ah and it rarely drops below 80% overnight even with lights, a small 12v fridge and charging devices.

The thing people underestimate is that with lithium you're only really using ~80-90% usable capacity anyway, so "overkill" quickly becomes "actually fine."

What's your solar situation? A single 200W panel in a UK winter will struggle to keep 200Ah topped up during cloudy stretches. That's where most people come unstuck — matching the panel array to the battery, not just the battery size itself.

@BordersOffGrid worth thinking about what you're actually running in there. Lighting and phone charging is barely going to dent a 200Ah bank, but if you're adding a 12v compressor fridge or any kind of heating (even a small fan heater on an inverter), you'll be grateful for every amp-hour you've got.

One thing I'd flag — with a shepherd's hut you're unlikely to have huge roof space for solar, so charging capacity matters as much as storage. A smaller battery that charges quickly and fully every day will often serve you better than a big bank that sits at 60% all winter.

What's your solar panel situation looking like? That might be the more interesting constraint to work around first.

@BordersOffGrid one thing worth adding to what's already been said — think about your charging source as well as the battery itself. A 200Ah lithium wants a decent solar input to keep it topped up properly, especially through autumn and winter up in the Borders where you might go several grey days in a row. I'd suggest pairing it with at least 300-400W of panels if you can manage it on the hut roof. Also worth checking that whatever charge controller you go for has a proper lithium charging profile — some of the cheaper units don't handle LiFePO4 particularly well and you'll end up undercharging. Gets asked a lot on here and it's an easy thing to overlook when you're focused on the battery itself.