Anyone else running a small cabin on a single 100Ah LiFePO4 with a mix of 12V and 240V loads?

Finally got my 6x6m timber cabin wired up last weekend and I'm trying to work out whether my setup is going to cut it through winter. Running a single 100Ah LiFePO4 (Fogstar Drift), charged via two 200W panels on a Victron 75/15 MPPT. Loads are pretty light — a 12V LED strip, a small 12V fridge (Brass Monkey, about 40Ah/day), phone and laptop charging, and occasionally a 240V kettle and lamp through a 300W pure sine inverter.

The summer has been absolutely fine, but I'm starting to stress about the shorter days. At best I'm probably looking at 2–3 peak sun hours in December up here in the Peak District, which on a good day gives me maybe 60–80Ah back in. Fine on paper until you factor in the fridge running overnight and a couple of grey days back to back.

I'm wondering if anyone's been in a similar situation and whether they just added a second battery or went straight to a small generator for backup. I've been eyeing up a Honda EU22i but that feels like a big spend just for occasional top-ups. Is a second 100Ah Fogstar the more sensible first step, or am I missing something obvious?

SomersetOffGrid | Posts: 847 | Location: Somerset (obviously)

@Squib30 Nice one, Fogstar Drift is a solid choice for the money. Winter is where it gets interesting though - worth doing a proper load audit before you're caught short in December.

Quick tip: if you haven't already, grab a Victron SmartShunt so you can actually see what's being consumed in real time rather than guessing. Makes a massive difference to how you manage things.

The 240V loads are usually the killer - even a small inverter sat idle can chew through 1-2A at 12V. What are you actually running through the inverter? Laptop, occasional power tools, or something heavier? 100Ah is workable for light use but you'll want to know your daily consumption figures before committing.

What's your charging source - solar, alternator, hook-up?

CliveKnight | Posts: 312 | Location: Afloat, mostly

The 12V/240V split is exactly where people trip up. On my shepherd's hut I learned this the hard way — the inverter sitting idle was quietly chewing through maybe 8-10% of that 100Ah daily just on standby draw. Switched everything I could to native 12V (lighting, USB charging, a little 12V compressor fridge) and only fire up the inverter for the occasional drill or laptop brick that genuinely needs 240V.

That single discipline bought me back roughly 15-20Ah per day, which in a short winter where your panels might only deliver 20-30Ah anyway, is the difference between making it through and waking up to a low-voltage cutoff.

@Squib30 what's actually on the 240V side? If it's just a couple of things, there may be native 12V alternatives worth considering before you start eyeing a second battery.

LindaGrant | Posts: 1,203 | Location: Derbyshire

@Squib30 Worth being really precise about your 240V loads before assuming the battery will cope. Inverters have a standing draw even with nothing running - mine pulls about 8W just sitting idle, which adds up overnight. If you can shift anything to native 12V (lighting especially), you'll thank yourself come February when the panels are barely scraping 2-3 hours of decent output.

Also, what's your solar input? A 100Ah LiFePO4 is roughly 1.28kWh usable, which sounds reasonable until you factor in a proper winter week of overcast days up here in the Midlands. Are you planning a generator backup at all, or relying purely on solar? That's really the crux of whether it'll cut it rather than the battery itself.

ExPostie | Posts: 634 | Location: Array

One thing nobody's mentioned yet — a single 100Ah at 12V is only 1.2kWh usable (assuming 80% DoD on the Drift). Run the numbers on your 240V loads carefully because your inverter alone will chew through standby draw even when nothing's switched on.

On my shepherds hut I was losing nearly 15-20Ah overnight before I realised the inverter was sitting idle drawing 1.5A continuously. Switched to a Victron Multiplus with auto-sleep and it transformed my overnight figures.

Winter's the real test — what's your panel setup? One 100Ah through a UK December with anything less than 400W of panels is going to leave you in deficit more days than not. Been there.