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

Got a bit of a specific situation here and wondered if anyone had real-world experience rather than just spreadsheet maths.

I'm setting up a small garden office with a 200Ah LiFePO4 (Fogstar Drift 12V) and around 400W of solar on the roof. The office itself is fine during the day but I've been thinking about adding a small chest freezer — something like a 60-70L unit — partly for convenience and partly as part of a wider emergency backup plan for the house.

My concern is overnight performance. I know chest freezers cycle on and off rather than running continuously, but I've seen wildly different figures thrown around for consumption. Some people say a small unit pulls around 100-150Wh per 24 hours if it's reasonably full and the ambient temperature isn't mad. Others seem to suggest double that.

So realistically, would a 200Ah (roughly 2.4kWh usable at 80% DoD on LiFePO4) cope overnight — say 10-12 hours — without the solar doing anything? Or is it marginal enough that I'd be pushing my luck, especially in winter when ambient temps in an unheated space might actually help the freezer but the solar recovery the next day is weak?

Also wondering whether the inverter efficiency loss is significant enough to factor in heavily here. Running 12V through a Victron Phoenix 375VA at the moment.

Anyone actually measured their freezer draw with a plug-in energy monitor rather than just going off the spec sheet?

@DaiLewis69 Running a chest freezer on my narrowboat so got some relevant experience here. What's the wattage on the freezer? That's the key question — chest freezers vary massively. Mine pulls around 30-40W average (they cycle on and off), so overnight say 10 hours is roughly 300-400Wh. On a 12V 200Ah Fogstar that's around 2.4kWh usable, so theoretically comfortable.

But what's your ambient temperature? A garden office in winter means the freezer works harder. Also worth checking the compressor startup surge — does your inverter handle that?

What inverter are you pairing with it?

Depends heavily on the freezer. A decent small chest freezer (like a Inventor or Subcold) pulls maybe 30-50W average — sounds great until you factor in the compressor startup surge and how often it cycles in a warm garden office.

200Ah at 12V is 2.4kWh usable if you're genuinely pulling the full 100% — but LiFePO4 you'd want to keep above 20% realistically, so call it ~1.9kWh.

Overnight at 8 hours? Should be fine in winter. Summer in a poorly ventilated outbuilding is a different story — freezers work harder, cycle more frequently.

What I'd actually question is whether your inverter is sized properly for the startup surge. Undersized inverter is where people come unstuck, not the battery capacity. What are you running?

Good question to ask before committing. One thing worth adding to what @ExPostie said — ambient temperature matters enormously with chest freezers. In a garden office that drops to 5°C overnight, the compressor barely runs. Same freezer in summer hitting 30°C inside the office could double that average draw.

Also worth checking: does your Fogstar Drift have low-temperature cutoff? Some LiFePO4 cells won't discharge below a certain point, which could cause unexpected shutdowns if the office gets properly cold.

What's your solar/charging situation? A 200Ah battery running a freezer overnight is probably fine, but if you've got no way to replenish it the following day (consecutive cloudy days in the UK being rather common...), you might find yourself in trouble within 48 hours.

@ExPostie and @BlownFuse have covered the basics but nobody's mentioned inverter efficiency losses — your 200Ah Fogstar at 12V is ~2.4kWh usable (80% DoD), but shove that through a cheap inverter and you're losing another 10-15% before it even reaches the freezer.

Had the exact same setup in my motorhome last summer — Victron inverter made a noticeable difference over the cheap Amazon jobbie I started with.

Also worth knowing: chest freezers generally behave better than uprights on intermittent/solar power because the cold mass holds temperature longer during compressor off-cycles — so if you're pre-cooling it properly before nightfall you'll stretch that 200Ah considerably further than the raw numbers suggest.

Biggest real-world killer is actually lid discipline — every time someone opens it, your compressor runtime spikes.