Been wondering the same thing actually — I'm in a similar position with a small off-grid setup and trying to figure out the right battery sizing.
My situation: I'm primarily interested in keeping an EV charged up from solar, which obviously dominates any load calculation I try to do. But for a shepherd's hut specifically, if you're not doing EV charging, the loads are generally pretty modest aren't they? Lighting, a 12V compressor fridge, maybe a small inverter for a laptop — you'd struggle to pull more than 20-30Ah on a typical evening.
So the question becomes: what's your worst-case scenario for days without decent sun? Here in the UK, February can give you almost nothing for days on end. A 100Ah Fogstar Drift would probably serve a basic hut setup fine, with enough buffer for a few cloudy days.
That said, the argument for 200Ah is the cycle longevity — lithium doesn't mind sitting at partial state of charge, but oversizing means you're never hammering the battery hard, which should extend its life considerably.
A few things worth knowing before deciding:
- What's your solar array size? Battery should be roughly matched to what you can actually charge in a day
- Are you running a proper inverter, or just 12V DC loads?
- Will the hut be occupied year-round or seasonal?
What inverter/charger setup are you running with it? And is this a Victron-based system or something simpler? That might affect the answer — some of the smaller Victron kit has minimum battery size recommendations.
