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

Running a small chest freezer (the Argos 30L job) in my motorhome and trying to work out if my current battery bank will cope overnight without solar input — so roughly 10–12 hours of darkness.

The freezer pulls around 35–45W when the compressor cycles, but obviously it's not running continuously. From what I've read, these small units tend to have a duty cycle somewhere around 30–50% depending on ambient temperature, which in a British summer probably sits at 40% realistically.

So my rough calculation:

• Average draw: ~40W × 40% duty cycle = ~16W average
• Over 12 hours: 16 × 12 = 192Wh
• At 12V: roughly 16Ah consumed

That seems well within what a 200Ah lithium (Fogstar Drift is what I'm running) should handle, given you can realistically use 80–90% of rated capacity. That's 160–180Ah usable, so the freezer overnight looks trivial on paper.

But here's what I'm less certain about:

1. Does ambient temperature inside the motorhome significantly change that duty cycle? If it's 25°C inside overnight, is the compressor running much harder?
2. Are there any start-up surge considerations for the inverter that might cause BMS trips on a single 200Ah cell?
3. Anyone running this kind of setup with a Victron MultiPlus or similar and seen unexpected issues?

I've got a 1000W Victron inverter in the loop, so power delivery shouldn't be the bottleneck — just want to sense-check the capacity maths before I commit to leaving it running unattended overnight

@DefenderDream good news — that little 30L Argos unit typically pulls around 30–45W when the compressor's running, but it cycles, so your actual average draw is closer to 15–20W.

Over 12 hours that's roughly 180–240Wh.

On a 200Ah lithium (assuming 12V and usable capacity to 80% DoD), you've got around 1,920Wh available — so the freezer alone is barely touching it.

Worth noting:

• Ambient temperature massively affects compressor duty cycle
• Pre-chill everything before disconnecting from hookup
• A Victron BMV-712 will give you real consumption data after a night or two

I ran a similar setup last winter touring Scotland with a Fogstar 200Ah cell and was genuinely surprised how little the freezer consumed compared to my inverter loads. The freezer was almost a non-issue.

Your bigger overnight enemy is probably lighting and heating, not the freezer.

@VivaroWanderer has done the wattage maths already so I'll spare you — but don't forget your usable capacity isn't the full 200Ah unless you fancy a very warm freezer and a very dead Fogstar at 3am! 🧊

Factor in your inverter losses too if you're not running it on 12V direct, because nothing says "surprise breakfast" like a thawed bag of sausages at dawn.

@RetiredNurse49 makes a solid point on usable capacity — worth adding that with a single 200Ah LiFePO4 you're looking at roughly 160–180Ah usable depending on your BMS cutoff.

Quick real-world check: I ran a similar setup last winter with a Fogstar Drift 200Ah and a small compressor fridge. Survived 11 hours no bother, woke up to about 40% remaining.

One thing nobody's mentioned — ambient temp matters a lot. Freezer works harder if your van gets warm overnight, so if you're parked somewhere mild you'll use less than worst case.

200Ah should be fine for one night but I'd be nervous about two consecutive cloudy days without any solar or hook-up to top it back up.

@Wayne1980 @RetiredNurse49 good points all round — one thing nobody's mentioned yet is the ambient temperature in the motorhome overnight. Running mine in the van last summer, the freezer was cycling way more frequently because the surrounding air was warm, which pushed consumption up noticeably compared to the manufacturer's quoted figures.

Also worth checking what BMS your battery has — I've got a Fogstar Drift 200Ah and its low-temp cutoff caught me out once when it got properly cold. Woke up to a warm freezer and a confused BMS.

Might be worth chucking a Victron SmartShunt on if you haven't already — gives you proper real-world data over a few nights rather than guessing from specs.