Anyone know if a 200Ah lithium battery will run a small chest freezer overnight?

Running a small chest freezer off-grid is something I've been mulling over for the boat, so curious whether anyone's actually done the maths on this properly.

My situation: I've got a 200Ah LiFePO4 (Fogstar Drift) sitting in the garden office setup, and over winter I'm planning to repurpose some of that capacity for a small chest freezer — something like a 60-litre unit. The office draws very little overnight, so theoretically there should be headroom.

From what I can work out, a decent small chest freezer might pull around 30-40W when the compressor's running, but obviously it cycles on and off rather than running continuously. I've seen figures suggesting maybe 0.5–1 kWh per 24 hours for a well-insulated unit, which on paper looks manageable.

What I can't quite figure out:

• How much of that 200Ah is realistically usable overnight without hammering the battery (staying above 20% SOC)?
• Does the compressor start-up draw cause any issues with a standard 1000W inverter?
• Is there a meaningful difference between running a purpose-built 12V compressor fridge versus a mains chest freezer through an inverter, efficiency-wise?

I've got Victron kit managing everything, so the monitoring side is covered — I just don't want to find out the hard way that I've been naive about the actual consumption figures.

Anyone running something similar, either on a boat or off-grid building? Real-world numbers would be far more useful than spec sheets at this point.

@FormerMariner36 really depends on the freezer's actual consumption rather than its rated wattage — they cycle on and off so the duty cycle matters massively. Have you checked if yours has an energy label with kWh/24hrs? That's the most reliable starting point.

For my garden office setup I use a Fogstar Drift 200Ah and I've found real-world draw is always higher than I'd budgeted for once you factor in ambient temperature (freezers work harder in warm weather).

A few questions worth thinking through:

• What's the freezer's actual kWh/24hr figure?
• What's your usable DoD — are you going to 80% or deeper?
• Any solar topping up overnight, or fully standalone?

200Ah could work but I'd want to see the numbers before committing. What freezer model is it?

Good point from @HollyGazer about actual consumption. From my cabin setup I'd add — ambient temperature matters massively. My chest freezer pulls maybe 30-40Wh per hour in a cool outbuilding, but when I had it in a warmer space that crept up considerably.

On a 200Ah LiFePO4 you've realistically got around 190Ah usable (LiFePO4 is brilliant for this). At 12V that's roughly 2.28kWh. A decent small chest freezer overnight (say 10 hours) might use 300-500Wh depending on ambient and how full it is.

You should be absolutely fine in most scenarios — that's only 15-25% of your capacity gone.

Fogstar do a decent 200Ah if you're shopping around. I'd also suggest a smart shunt (Victron BMV-712) so you actually know what's happening rather than guessing.

Ran this exact experiment on my narrowboat last summer. The chest freezer I had — a small 60L unit — was pulling around 30–40Ah per 24 hours in decent ambient temps, so overnight (say 8 hours) you're looking at roughly 10–15Ah in practice. Your 200Ah bank has that covered easily, even accounting for BMS overhead and only drawing to 80% usable capacity.

The variable nobody's mentioned yet is compressor start-up surge — worth checking your BMS can handle the brief spike without tripping. Most decent LiFePO4 packs manage it fine, but I've seen cheaper units hiccup on this.

Also worth fitting a small Victron BMV monitor if you haven't already — takes the guesswork out entirely and you'll actually know what your freezer costs you each night rather than estimating.

Great thread — this is exactly what I spent a sweaty August weekend testing in my shepherd's hut conversion.

One thing nobody's mentioned yet: duty cycle varies wildly by how full the freezer is. Mine ran noticeably longer between cycles once I'd packed it out with frozen water bottles. More thermal mass = less work for the compressor.

On a 200Ah LiFePO4 (assuming you're not dropping below 20% SOC) you've realistically got around 160Ah usable. A well-packed small chest freezer in moderate temps should sit comfortably within that overnight — but I'd stick a Victron SmartShunt on it first and actually log a 24-hour cycle before committing.

@PanelDan's narrowboat data is gold — ambient temps on a boat hull can be surprisingly forgiving in summer compared to a static caravan baking in direct sun.

Done this on both my garden office and the boat, so can chip in properly.

The maths that catches people out: it's not just the watt-hours, it's duty cycle vs ambient temp. A well-insulated chest freezer in a cool bilge space might only run 20-30% of the time. Same unit in a hot engine room or sunny cockpit locker? Could be 60%+.

On my boat I run a 40L Engel-style unit. Honest overnight draw (8hrs, cool environment) sits around 15-25Ah. Your 200Ah LiFePO4 — assuming you're not going below 20% SoC — gives you ~160Ah usable. So technically fine, but factor in your other loads too.

@PanelDan's narrowboat data sounds about right to me. Pre-cooling the freezer before you go off-grid makes a noticeable difference as well.