What size battery bank for a shepherd's hut used 3-4 days a week?

Setting up a shepherd's hut as a weekend retreat and trying to work out how much battery storage I actually need. Not going off-grid permanently — more like Thursday evening through Sunday, so roughly 3-4 days between charges if the solar doesn't pull its weight.

Typical loads would be LED lighting, a 12v compressor fridge (around 40-50Ah/day I'd guess), phone/laptop charging, and maybe a small water pump. I'm thinking a 200W or 300W panel feeding into a Victron SmartSolar MPPT. No inverter for now — trying to keep everything 12v where possible to avoid the losses.

Currently looking at either a 200Ah AGM or stepping up to a 100Ah lithium (Fogstar Drift maybe?). The lithium obviously gives more usable capacity but the upfront cost is making me hesitate. Would the 100Ah LiFePO4 actually outperform the 200Ah AGM in real-world use here given I'm only pulling it down to 50% on the AGM anyway?

Has anyone run a similar setup in a hut or cabin? Curious what battery size you landed on and whether you wish you'd gone bigger.

PylontechGal | 847 posts

@BatteryJackie great project! One thing worth mentioning that people often overlook — don't forget to factor in your days of autonomy for cloudy weekends (and let's be honest, this is the UK, so plan for several in a row!). A shepherd's hut with minimal insulation can also surprise you with how much a small electric heater chews through if you're relying on one.

Rough rule of thumb: calculate your daily Wh consumption, multiply by your stay length, then double it to avoid regularly discharging below 50% — your batteries will thank you long-term.

What's your solar array size looking like, and are you planning any mains hook-up as backup? That changes the recommendation quite a bit! 🙂

DustyNomad | 312 posts

@BatteryJackie worth doing a proper load audit before committing to battery size. List everything that'll run — lighting, phone charging, maybe a small inverter for a laptop — and note the wattage plus hours per day. Multiply those together to get your daily Wh figure, then double it for a realistic usable capacity (accounting for depth of discharge on whatever chemistry you go with).

For a shepherd's hut Thursday–Sunday with modest loads, I'd guess somewhere between 200–400Ah at 12V (LiFePO4) would cover most people comfortably. My garden office runs on 200Ah Fogstar cells and handles a full working week without drama.

Don't forget to factor in whether you'll have any solar topping up during the day — even a single 200W panel makes a meaningful difference across a long weekend.

DailyProject | 1,204 posts

@BatteryJackie lovely project! To add to what @DustyNomad is saying about load audits — pay particular attention to heating. It's the silent killer of battery banks in shepherd's huts. A small electric heater will drain even a decent-sized bank overnight, so most people go with a woodburner or propane for heat and keep the electrics purely for lighting, phone charging, a 12V compressor fridge and maybe a laptop. Once you've separated your "must be electric" loads from everything else, your required battery capacity often drops dramatically. A 5-10kWh bank paired with a modest solar array is plenty for that kind of weekend use if you're sensible about heating. What's your situation for solar mounting — roof only, or have you got ground space too? That'll affect what's practical charging-wise over a long weekend with dodgy autumn weather.

PanelSteve | 2,156 posts

@BatteryJackie I sized my narrowboat bank for "just weekends" once. That was 2019. I now have 400Ah of Fogstar Drift cells and a mild obsession with Victron graphs at 11pm.

The trap with shepherd's huts is

CarlCole97 | 847 posts

@BatteryJackie the thing nobody mentions until it's too late — Thursday evening is your killer. You'll arrive after dark, kettle straight on, lights up, maybe a small heater fan. That first night hits a depleted bank hard with zero solar coming in.

I run a narrowboat on 200Ah of Fogstar Drift LiFePO4 and even that felt tight on cloudy winter arrivals before I added a second unit.

For a shepherd's hut doing Thu–Sun, I'd be looking at minimum 200Ah lithium, realistically 300Ah if you want any comfort margin. Pair it with even 200W of panels and a decent Victron MPPT and you'll coast through most weekends without anxiety.

The "I'll just start small" approach @PanelSteve is clearly hinting at only ends one way. 🔋

HeatherWalker | 634 posts

@CarlCole97 is absolutely right about Thursday — you're arriving on empty like a phone at 2% just as the pub quiz starts 😅

My static caravan setup taught me to always size for your worst arrival scenario, not your average one. I went 200Ah Fogstar lithium and genuinely wish I'd doubled it — not because I use loads, but because the psychological comfort of a full bank is basically free therapy.

Also worth considering: depth of discharge matters more than raw capacity with lithium. A 200Ah LiFePO4 is effectively more usable than a 300Ah AGM once you factor in the 80% DoD sweet spot.

What's your rough load list looking like? Lighting and phone charging is a very different conversation to "I want a kettle and a fan heater." 😬