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

Running a small chest freezer off-grid is something I've been mulling over for the boat, so I'm curious whether anyone's actually done the maths on this properly.

My setup currently has a single 200Ah lithium (Fogstar Drift 12V) paired with a modest solar array — enough to keep lights, a 12V compressor fridge, and a few small loads ticking over. But I'm thinking about swapping the compressor fridge for a small chest freezer conversion, mostly because they're supposed to be far more efficient once the lid seal is good.

The chest freezer I'm looking at is a 60-litre unit rated at around 100W. Obviously it won't be running continuously — duty cycle is where it gets interesting — but I'm struggling to find reliable real-world figures for overnight consumption, say from 10pm to 7am.

A few specific questions:

• Has anyone actually logged overnight draw on a similar setup?
• Does ambient temperature make a dramatic difference to duty cycle? (The boat can get cold overnight, which should help, but summers are another story.)
• Would 200Ah at 80% usable capacity — so roughly 160Ah — realistically cover it, or am I cutting it too fine without daytime solar topping things back up?

I'd rather not size up to a second battery if I can avoid it, purely for space and weight reasons on the boat. But equally I don't want to discover mid-July that I'm flattening the bank every night.

Anyone who's run a chest freezer conversion off a similar bank, even in a garden office or van setup, I'd love to hear what you actually experienced rather than just the spec sheet estimates.

@CallumHobbs welcome to the forum mate, good first question! 🎉

Running a chest freezer overnight is very doable from 200Ah lithium — I've been doing exactly this on my boat for two seasons now.

Key thing people miss: chest freezers are incredibly efficient because cold air doesn't fall out when you open them. Mine pulls maybe 150-200Wh per 24hrs once it's pre-cooled.

Quick rough maths:

• 200Ah @ 12V = 2400Wh usable (assuming Fogstar or similar LiFePO4 at ~100% DoD)
• Overnight (8hrs) freezer draw ≈ 60-80Wh

You'll be absolutely fine.

Top tip though — pre-cool the freezer on shore power or solar before switching to battery, makes a massive difference to overnight consumption.

What size freezer are you looking at?

@CallumHobbs I've done exactly this on my boat with a 200Ah Fogstar Drift LiFePO4. A decent small chest freezer (think Shoreline or Isotherm) draws around 30–50Wh average over 24hrs depending on ambient temp and insulation quality — so overnight is comfortably achievable.

The bit people miss is compressor start-up surge — make sure your inverter can handle 3–4x the running wattage momentarily. Had a cheap inverter trip out on me before I upgraded.

Also worth checking your freezer's thermostat cycling frequency. In summer on a warm boat, it'll run harder. I'd say 200Ah gives you decent headroom overnight, but I wouldn't push it below 20% SOC habitually — LiFePO4 likes it if you don't bottom it out regularly.

What inverter are you running?

@CallumHobbs done this on my narrowboat for two years — the secret weapon is a good quality freezer with thick insulation, because a poorly insulated box will eat your battery alive faster than you can say "where's my Victron app."

Key thing nobody's mentioned: pre-chill your freezer before going off-grid so it's not working overtime from warm. Also worth chucking a thermal mass inside (frozen water bottles etc.) to help hold temperature during the night when it cycles less frequently.

Your 200Ah LiFePO4 should be absolutely fine as long as you're not also trying to run a kettle and charge your phone simultaneously off the same bank. 😄

The maths that nobody mentions: a chest freezer's average draw is roughly 1/3 of its rated wattage once you account for compressor duty cycle — so a "60W" unit is really pulling ~20Wh per hour, meaning ~160Wh overnight. Your 200Ah LiFePO4 (at 12V, usable 80%) gives you ~1,920Wh — you're barely scratching it. 🧊

The actual enemy isn't capacity, it's inverter idle draw if you're running AC. Go 12V compressor fridge/freezer (Alpicool, Brass Monkey, or proper marine units) and you'll sidestep that loss entirely. My Victron SmartShunt confirmed I was wasting ~15Wh/hr just keeping an inverter ticking over — daft.

Short answer: yes, comfortably. Just don't use an AC freezer through a cheap inverter or @JimWilson's 20% figure starts looking optimistic rather than conservative.