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

Got a static caravan on a site in North Wales that I use as a semi-permanent base, and I'm trying to work out if my setup can handle keeping a small chest freezer running through the night without grid power.

Currently running a 200Ah LiFePO4 (Fogstar Drift) with a Victron SmartSolar MPPT handling the charging during the day. Solar input is decent in summer but obviously grim from October onwards.

The freezer is a Lec 100-litre chest freezer — rated at about 90W but obviously it doesn't run continuously. I've seen figures suggesting chest freezers cycle maybe 30-40% of the time depending on ambient temp and how full they are.

So rough maths in my head:

• 90W × ~10 hours × 35% duty cycle = ~315Wh
• 200Ah at 12V = 2,400Wh usable (assuming ~80% DoD on the lithium)

On paper that looks absolutely fine, almost embarrassingly comfortable. But I've been caught out before thinking something was straightforward and then finding out there's a variable I hadn't considered — inverter losses, the freezer pulling a startup surge, ambient temp hammering the duty cycle in a heatwave, that sort of thing.

Has anyone actually measured their chest freezer draw overnight using a proper energy monitor? Wondering if my duty cycle assumption is wildly optimistic or if I'm in the right ballpark.

Running a Victron MultiPlus 12/1200 as the inverter so surge capacity shouldn't be an issue, but curious whether anyone's seen unusual consumption patterns with chest freezers specifically.

@FellKev ran almost exactly this experiment in my shepherd's hut two summers back — short answer is it depends on the freezer.

A decent modern chest freezer (say, 60–100L) typically pulls somewhere between 30–60Wh per hour once it's up to temperature, so overnight (8–10 hours) you're looking at roughly 300–500Wh total draw.

A 200Ah lithium at 12V gives you around 2,400Wh usable — so yes, mathematically comfortable. The catch is your ambient temperature and how often the lid gets opened before dark.

Mine runs through the night on a Fogstar Drift 200Ah without drama. The startup surge is the thing to watch — make sure your inverter (if you're running AC) can handle the compressor kick.

What inverter have you got, and is the freezer 12V direct or AC?

@FellKev I've got a similar setup in my static — Fogstar Drift 200Ah and a small 60L chest freezer. Overnight (roughly 10pm–7am) it pulls maybe 30–50Ah depending on ambient temperature. So in theory 200Ah should be plenty, but that's assuming your battery is healthy and you're not simultaneously running anything else.

The killer is what state your battery is in before sunset. If you're going into the night below 80% SoC you could struggle, especially in a Welsh November.

What inverter are you running? Some cheaper units have high idle draw which silently eats into your overnight budget more than the freezer itself does.

The dirty secret nobody mentions: chest freezer efficiency tanks if it's sitting in a warm caravan — ambient temp sends compressor duty cycle through the roof, so @FellKev's North Wales location is actually working in your favour come autumn/winter nights.

On the narrowboat I run a Victron SmartShunt and the overnight draw data genuinely transformed how I sized my battery bank — worth every penny just for the insight before you commit to anything bigger.

200Ah lithium (usable ~180Ah) should be fine in Welsh conditions, but I'd log a few nights' data before declaring victory.

@FellKev one thing nobody's touched on yet: compressor duty cycle is everything here, and it varies wildly between freezer models.

A decent inverter-compressor unit (Alpicool, Brass Monkey etc.) might only pull 35–45W average when it's properly loaded and the ambient isn't silly. A cheap resistive-thermostat job could be drawing 80W+ average.

Run the maths: 80W × 8hrs = 640Wh. From a 200Ah/12V (2,400Wh) Fogstar or equivalent, that's 27% DoD — totally fine. But that assumes you're not also running lighting, a phone charger, and forgetting the inverter itself has standby losses.

@Spud's point about ambient is critical in a static too — that thin GRP skin offers almost no insulation. If it's baking in summer sun, your freezer is fighting hard.

Stick a plug-in energy monitor on it for 24hrs before committing. Actual data beats forum speculation every time, including mine.