Anyone else struggling to keep a 12v compressor fridge running overnight on 100ah lithium?

Narrowboat life sorted this one out for me sharpish — 100Ah is basically just about adequate if your fridge is halfway decent and you're not in the Arctic.

Few things that made the difference on my setup:

• Fridge placement matters more than people admit — shove it against a warm wall or in direct sun and you've essentially got a heater with a salad compartment
• Battery quality is everything — my old "100Ah" budget cells were doing about 70Ah in real life before the BMS threw a wobbler
• Switched to Fogstar Drift cells and suddenly the maths actually worked out

The compressor itself is the other variable nobody wants to talk about. A knackered or undersized compressor runs constantly instead of cycling properly, and at that point 100Ah might as well be a 9V battery.

What fridge are you actually running? The difference between a Dometic CFX and some no-name unit off Amazon is roughly the difference between "fine overnight" and "warm beer and a bad morning."

Also — are you monitoring properly? Chucked a Victron BMV-712 on mine and spent a genuinely embarrassing amount of time just watching the screen instead of, y'know, going anywhere.

What's your solar situation looking like? Even a modest 200W panel makes overnight anxiety basically disappear if you had a decent day beforehand.

@EssexNomad mate, static caravan life taught me that 100Ah lithium and a compressor fridge is basically a game of "who blinks first" — and in January on a north-facing pitch, the fridge always wins.

Slapped a Fogstar 200Ah under the van seat and suddenly I stopped rationing cheese like it was 1940s Britain.

@EssexNomad 100Ah lithium and a compressor fridge is basically a Victron BMV-712 telling you uncomfortable truths about your life choices at 3am.

@EssexNomad narrowboat experience here too — the variable nobody mentions is duty cycle vs ambient temperature. A quality compressor fridge (I run an Isotherm SR30) might only pull 4–5A when cycling, but in a warm engine room or south-facing boat that duty cycle creeps from 30% toward 60%+, effectively doubling your overnight draw.

On my setup I fitted a 10mm reflective foam panel behind the fridge cabinet and dropped consumption measurably — embarrassingly simple fix.

Also worth checking: is your 100Ah actually delivering 100Ah? Fogstar cells are solid but a poorly spot-welded DIY pack or a budget LiFePO4 with weak BMS will throttle output under sustained load. The Victron BMV will show you voltage sag under load which is the tell.

Ambient insulation first, then question your actual usable capacity before chasing bigger batteries.

@FenlandSolar that duty cycle point is really interesting — do you have any rough figures for how much the duty cycle changes between, say, a mild UK summer night versus a cold autumn one? I'm trying to work out whether my setup on the tiny house is actually undersized or whether I've just been unlucky with a warm spell.

I'm running a Fogstar 100Ah with a cheap Alpicool unit and honestly the overnight draw seems wildly inconsistent. Some mornings the Victron BMV shows I've barely touched 20Ah, other times I've pulled nearly 50Ah and I genuinely can't work out why. Same ambient temperature as far as I can tell. Could fridge contents (how full it is, how cold the food already is) really account for that much variation?