Does anyone know if a 200Ah lithium battery can run a small chest freezer overnight?

Running my narrowboat through another blistering British summer (both days of it), so this feels like a timely question for me too!

I've got a Fogstar Drift 200Ah sitting under my galley bench and I've been eyeing up a small chest freezer — something in the 30-50 litre range — to replace the icebox situation I've been tolerating like some kind of medieval peasant.

From what I've been reading, a decent well-insulated chest freezer in that size range might pull anywhere from 0.3 to 0.8 kWh over a full night, depending on ambient temperature and how often it cycles. On paper, a 200Ah lithium at 12V gives you roughly 2.4 kWh usable (assuming you're not flogging it below 20%), so the maths seems encouraging.

But here's where my brain starts itching:

• Does the compressor start-up surge cause any grief with a standard inverter setup? I'm running a Victron Phoenix 12/800
• Would a 12V compressor freezer (like an Alpicool or similar) be more sensible than mains-via-inverter?
• What's the real-world draw like once the thing is actually cold versus initial cool-down?

The narrowboat doesn't move every day, so I can't always guarantee solar top-up — I've got 200W of panels on the roof but November isn't exactly the Sahara, is it.

Anyone actually running this combination who can share some honest numbers rather than the rosy figures manufacturers put on the box?

@RetiredChef ha, the British summer struggle is real!

Done exactly this in my motorhome with a Fogstar Drift 200Ah — ran a small Subcold 35L chest freezer through the night and it was absolutely fine. Chest freezers are brilliant for this because once the contents are properly frozen, they barely cycle. Mine was pulling maybe 15-20Ah overnight in mild weather, so well within the battery's usable capacity.

The caveats though:

• Ambient temperature matters enormously — a hot engine bay or poorly ventilated space makes the compressor work much harder
• Make sure your freezer is actually full (water bottles fill gaps brilliantly)
• Check your compressor's starting surge doesn't upset your inverter

What freezer are you looking at? That'll make a big difference to the actual draw figures.

@RetiredChef my shepherd's hut Fogstar does this no bother — just don't open the freezer every five minutes to check if it's still frozen, because apparently that's "not how fridges work" according to my wife.

Great question, and sounds like you've already got the right battery for it! One thing worth adding — pre-cooling your freezer contents before you rely solely on battery power makes a noticeable difference to overnight consumption. A well-stocked freezer also holds temperature far better than a half-empty one, so if yours is looking sparse, chuck some frozen water bottles in to fill the gaps.

Also worth checking your freezer's ambient temperature rating. Some chest freezers struggle to run efficiently when the surrounding air is warm (ironic given our summers, but worth knowing if you're below deck where it can get stuffy).

@TorFinn makes a fair point about lid discipline too — every peek costs you more than you'd think. With sensible usage you should be absolutely fine overnight on that 200Ah. What's the freezer model out of curiosity?

@RetiredChef the numbers stack up nicely for you. A chest freezer typically pulls 30–80W running average (compressor duty cycle included), so overnight — call it 10 hours — you're looking at 300–800Wh consumed. Your 200Ah Fogstar at 12V is sitting on roughly 2.4kWh usable (assuming 80% DoD), so even a hungry freezer only bites off a third of your capacity.

The variable nobody mentions: ambient temperature. A narrowboat galley in July — even our two days of summer — can push the compressor to work considerably harder. Stick a thermometer near the unit and see what it's actually drawing with a cheap inline watt meter. I ran one on my setup for a week before I trusted the maths.

If you're not already running a BMV-712 or similar battery monitor, that'd be my first investment before worrying about anything else.