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

Got a Fogstar Drift 200Ah sat on my narrowboat doing sterling work running the lights and a few USB gadgets, but I'm eyeing up a small chest freezer (looking at the Subcold Ultra 35L) and wondering if my setup can actually handle it overnight without waking up to warm fish fingers.

Few specifics that might help anyone with the maths:

• Battery: Fogstar Drift 200Ah LiFePO4 (so realistically ~180Ah usable before I'd want to stop drawing)
• Charging: Single 200W solar panel via a Victron SmartSolar MPPT — which in a British winter is obviously doing the work of a chocolate teapot
• Inverter: Victron Phoenix 12/1200

From what I can work out, a 35L chest freezer draws roughly 30–45W when the compressor kicks in, with maybe a 25–30% duty cycle in a cool ambient temperature, so we're talking perhaps 80–120Wh per night? That sounds like it should be well within range, but I've been wrong before — ask my ex-wife about the canal trip incident.

Main uncertainties I can't quite nail down:

1. Does the compressor startup draw cause any meaningful spike that a 1200W inverter would struggle with?
2. Does ambient temperature on the boat (could get down to 5°C in the cabin overnight) actually help significantly with freezer efficiency, or does it introduce other issues?
3. Am I missing anything obvious that'll make me look a proper muppet?

Anyone running something similar? Real-world consumption figures would be far more useful than manufacturer specs, which seem to have been written by optimistic elves

@OldSailor the Subcold Ultra 35L pulls around 60-80W when the compressor kicks in, but average consumption is typically 15-20Wh per hour once it's down to temperature — so roughly 360-480Wh over 24 hours.

Your 200Ah Fogstar at 12V gives you ~2400Wh theoretical, but you realistically want to stay above 20% SOC with lithium, so call it ~1920Wh usable.

Overnight (8-10 hours) you're looking at 150-200Wh — well within budget if the freezer is already cold when you start. Pre-cooling before your solar input drops is the key habit to develop.

The gotcha on narrowboats is ambient temperature swings — a warm engine room will hammer compressor run-time. Where are you planning to site it?

I ran a similar setup in my shepherd's hut last summer without issue on a 100Ah, so 200Ah should be very comfortable.

@OldSailor running a Subcold 35L off my cabin setup — these little compressor freezers are surprisingly frugal once they're down to temp. Reckon you're looking at maybe 20-30Ah overnight realistically, so your 200Ah Drift has masses of headroom.

Main thing to watch on a narrowboat is ventilation around the freezer — they work harder in a warm engine bay. Also worth keeping an eye on your low voltage cutoff, especially in winter when you're not getting much solar topping things up.

Should be absolutely fine though.

Run the numbers first before getting excited — that's my golden rule.

Your 200Ah at 12V gives you roughly 2,400Wh, but usable capacity on a Drift is around 80%, so call it ~1,920Wh in practice.

The Subcold 35L typically averages 15-25Wh over 24 hours once it's at temp — so overnight (say 8 hours) you're looking at maybe 100-170Wh worst case. That's barely a dent.

The trap @OldSailor is the pull-down phase — if you load it warm, that compressor runs almost continuously for the first hour or two, which stings harder. Pre-chill contents before switching it over.

Real concern on a narrowboat is charging recovery. What's your solar or alternator situation? A freezer is a 24/7 load. The overnight maths are fine; it's cloudy weeks that'll catch you out.

Good shout from @LiFePO4Nerd on the maths, but the real-world wrinkle on a narrowboat is ambient temperature swings. Running my shepherd's hut setup through last winter, I noticed the freezer compressor kicked in far less frequently once the ambient dropped — essentially the cold air does some of the work for you.

The Fogstar Drift is a solid LiFePO4 unit, so you've got genuine usable capacity there without the usual lead-acid nonsense of only accessing 50%.

One thing worth factoring in: what's your charging situation overnight? On the cut, if you're not running the engine or hooked to shore power, that 200Ah is doing it alone until morning. A small 100W solar panel kept mine ticking over nicely through spring and autumn, but winter nights on the water are a different beast entirely.