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

Running a small chest freezer off my Fogstar Drift 200Ah overnight is something I'm genuinely curious about before I commit to wiring it up properly in my garden office setup.

The freezer is a 60L chest freezer — one of those cheap Russell Hobbs jobs. Rated at about 90W but obviously it cycles on and off rather than running flat out.

From what I can work out:

• Typical duty cycle on a small chest freezer seems to be around 25-35%?
• So maybe 25-30Wh actual consumption per hour
• Over 10 hours that's roughly 250-300Wh
• 200Ah at 12V = 2400Wh theoretical, but you'd only want to pull ~80% from lithium realistically = ~1920Wh usable

On paper it looks very comfortable, but I'm skeptical because:

1. I don't fully trust my duty cycle estimate — anyone actually measured theirs?
2. UK ambient temps vary massively. My office gets cold in winter, which should help, but summer could push the compressor harder
3. Inrush current on startup — is 200Ah enough to handle that without a beefy inverter?

Currently running a Victron SmartShunt so I could actually log real consumption once it's connected, but wanted a gut-check from people who've actually done this before I start drilling holes.

Anyone running something similar? Especially interested if you've got solar topping it up during the day or if it's purely battery overnight.

@CotswoldExplorer depends massively on the freezer's actual draw and how well insulated it is. A decent small chest freezer might only pull 30-50W when running but the compressor cycles on and off — so you're not drawing that constantly.

Rough maths: if it averages say 40W over 8 hours that's 320Wh, which your 200Ah (at 12V = 2400Wh usable to ~80%) should handle fine with headroom to spare.

Done similar on my boat with a Vitrifrigo chest fridge. Key thing is ambient temp — colder nights mean the compressor runs less.

Worth sticking a plug-in energy monitor on it for 24hrs before committing, gives you the actual numbers rather than guessing from specs.

Good question, and one I've been working through myself for my motorhome setup.

The key figure you need is the freezer's duty cycle — most small chest freezers don't run continuously. Typically they're compressing maybe 30-50% of the time, so your actual overnight draw could be considerably less than the rated wattage suggests.

On a 200Ah Fogstar Drift (assuming 12V), you've got roughly 2.4kWh usable if you're keeping above 80% DoD. Worth checking:

• What's the freezer's annual kWh rating on the label? Divide by 8,760 hours for average draw
• What's ambient temperature in your garden office overnight?
• Is there a thermostat you can adjust to reduce compressor cycles?

Have you actually measured the freezer's consumption with a plug-in energy monitor before committing to the wiring? That'd give you real numbers rather than estimates.

Worth noting that chest freezers are way more efficient than uprights anyway — less cold air escapes when you open them. So you've already made a decent choice there.

On a Fogstar Drift 200Ah you've got roughly 180–190Ah usable before you're stressing the cells. A small chest freezer cycling properly in a well-insulated space might only pull 30–50Ah overnight depending on ambient temp. Summer nights in a garden office could push that up a bit though.

Had similar concerns when I wired mine into the van — ended up chucking a Victron BMV-712 on it just to actually see what the freezer was drawing over 24hrs. Took the guesswork out completely. Recommend doing that before committing to anything permanent.

Pre-cooling the freezer while still on mains before switching to battery overnight is an easy win too.

@CotswoldExplorer I ran a similar setup on my narrowboat for two winters before upgrading. The thing that caught me out wasn't the freezer's rated draw — it was the compressor startup surge hitting the BMS hard during cold mornings. Worth checking your Fogstar's continuous discharge rating against that surge figure.

Practically speaking: a 200Ah lithium at 12V gives you roughly 2.4kWh usable. A decent small chest freezer might only cycle 30–40% of the time, so actual overnight consumption is often 0.3–0.6kWh. You should be well within range.

One real-world tip — fill any empty space in the freezer with water bottles. Thermal mass keeps temperatures stable between compressor cycles, which means less runtime and less draw on your battery. Made a noticeable difference on my static caravan setup too.