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

Running a small chest freezer off-grid at my cabin and trying to work out whether a 200Ah lithium (LiFePO4) is realistically going to cover me overnight without the solar input.

The freezer is a Subcold Ultra 35 — rated at ~85W running power, but obviously the compressor cycles rather than runs continuously. From what I've read, a chest freezer of that size typically draws somewhere between 0.5–1.0 kWh per 24 hours depending on ambient temperature and how often it's opened.

My rough maths:

• 200Ah at 12V = 2.4 kWh usable (assuming I don't want to go below 20% SoC on the LiFePO4)
• Overnight = roughly 14 hours without solar (late October, Scotland)
• Freezer worst-case = ~0.6 kWh overnight

On paper that looks very comfortable, but I'm wondering if I'm missing something. A few specific questions:

1. Does compressor start-up surge cause any issues with a 12V inverter setup? I've got a Victron Phoenix 12/800 — should handle it, but not 100% certain.
2. Is ambient temperature in an uninsulated outbuilding going to reduce draw (compressor works less hard in a cold Scottish October) or cause other problems?
3. Anyone running a similar setup with Fogstar Drift or similar LiFePO4 cells who can share actual overnight consumption figures?

Basically trying to validate my calculations before I commit to leaving the freezer running unattended for a few nights. Any real-world data would be genuinely useful rather than just spec-sheet figures

@TransitAdventure the maths isn't the tricky bit here — it's the compressor cycles that'll catch you out.

My narrowboat runs a small chest freezer and I learned the hard way that the stated wattage means very little. What matters is how often that compressor kicks in, and for how long. A well-insulated chest freezer in a cold cabin overnight might cycle far less than the same unit on a warm summer night.

Rough working: if it's drawing 30-40W average, overnight (say 10 hours) that's 300-400Wh. On a 200Ah LiFePO4 (let's say ~2.5kWh usable), you're fine with headroom to spare.

But monitor it first. Stick a Shelly plug or similar energy monitor on it for a few days. Real data beats any estimate. You might be surprised — or you might not be.

Really interested in this thread because I've been wrestling with exactly the same question for my narrowboat setup!

@Spider makes a good point about compressor cycles — but can I ask, does the ambient temperature of where you're storing the freezer make a significant difference to how often it cycles? I'd imagine a chest freezer in a cold cabin overnight would cycle far less than one in a warm engine room...

Also @TransitAdventure, do you know the actual wattage of the compressor when it is running? That's the figure that really matters isn't it, rather than just the average draw? I've got a Victron SmartShunt and it's been really eye-opening seeing those spike loads on my boat.

Wondering if anyone has real-world data from overnight monitoring rather than just theoretical calcs?

@CraftyWelder

@TransitAdventure good question, and @Spider is absolutely right about the compressor cycles being the real wildcard. One thing worth adding — ambient temperature matters enormously with chest freezers. A cold cabin overnight actually works in your favour, as the compressor runs less frequently to maintain temperature.

A 200Ah LiFePO4 gives you roughly 2kWh usable (assuming you're not pushing it below 10%). Most small chest freezers average 30-60W actual consumption when you account for duty cycle, so overnight (say 10 hours) you're realistically looking at 300-600Wh used. Should be fine on paper.

That said, I'd stick a basic energy monitor on it for a few nights first — the Owl or similar — before committing to a setup. Real-world data beats any calculation.

@LindaClark90 narrowboat use is slightly different too, worth a separate thread!

Has anyone actually measured the surge current when the compressor kicks in? I've been curious whether that causes issues with the BMS on smaller lithium packs — my Fogstar Drift 100Ah trips occasionally when something draws a big spike on startup.

Also wondering what @TransitAdventure is using for battery management — is there a Victron BMV or similar on the system? Without proper monitoring you're basically guessing at your state of charge overnight, which makes the whole calculation a bit academic.

One thing I'd add to what's been said — ambient temperature at the cabin matters a lot too. A freezer working harder in summer heat will chew through capacity faster than the nameplate figures suggest.