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

Been wrestling with this one for a few weeks now and figured I'd ask here before I commit to anything.

I'm living in a 20ft tiny house on a rural plot in Wales, currently running a 200Ah LiFePO4 from Fogstar. Solar input varies wildly this time of year — some days I'm pulling decent watts, other days the panels are next to useless under cloud cover.

The chest freezer I'm looking at is a small Igenix 60-litre unit, rated at around 85W. On paper the maths seems straightforward enough, but I know real-world draw isn't that simple — duty cycles, ambient temperature, how full the freezer is, all that jazz.

My main worry is overnight. No solar coming in, battery sitting there doing the work alone. If I'm only using the 200Ah for the freezer (nothing else drawing), is there a realistic chance I'd wake up with meaningful charge left, or am I going to hammer the battery and wreck the cycle life trying?

A few specific things I'd love clarity on:

• What's a realistic overnight draw for a small chest freezer in winter conditions?
• Should I be looking at a dedicated battery bank for the freezer, separate from my domestic bank?
• Would a larger 280Ah cell swap make more sense, or is that just buying headroom I don't actually need?

I've had a look at various calculators online but they all seem aimed at American RV setups and the numbers never quite feel right for UK conditions and usage patterns.

Anyone done something similar? Particularly interested if you're running a tiny house setup rather than a van or boat.

Hey @ZI_Sparks, Wales represent! 🏴󠁧󠁢󠁷󠁬󠁳󠁿

The short answer is probably yes, but the devil's in the detail. Chest freezers are actually brilliant for off-grid because they cycle rather than run continuously - a decent efficient one might only pull 100-150Wh over a full night once it's already cold.

Key thing to check is the freezer's actual energy rating rather than its wattage - the running wattage figure is misleading because the compressor isn't on constantly.

Pre-cooling the freezer before sunset helps massively, and ambient temperature in Wales will actually work in your favour during cooler months.

What freezer model are you looking at? Some are far more efficient than others. A Kill-A-Watt meter or similar is worth borrowing before committing - measure actual consumption over 24 hours first rather than guessing from the spec sheet.

My Fogstar 200Ah on the narrowboat runs a small chest freezer no bother overnight — the secret nobody mentions is pre-cooling it properly before sunset so it's not playing catch-up all night on your precious stored watts.

Good points from @ThistleVicky and @SilverCaptain already, but worth being precise about the numbers here.

A "small" chest freezer is vague — duty cycle matters enormously. Most compact chest freezers draw 60-100W when the compressor runs, but only cycle maybe 20-30% of the time in a cool environment. So real-world consumption is often 1-1.5kWh per 24 hours.

Your 200Ah LiFePO4 holds roughly 2.56kWh usable (at 80% DoD, assuming 16V nominal — check your actual voltage). So overnight alone? Almost certainly fine.

The real question is what else is running alongside it, and how you're recharging. In Wales in winter, don't bank on consistent solar. What's your charging setup? If you're relying purely on panels with no backup, that's where the plan can unravel quickly regardless of battery capacity.

One thing I'd add from running my shepherd's hut — ambient temp makes a massive difference. My little chest freezer pulls way less in summer than it did last winter when it was cycling constantly just to maintain temp in the cold. Counterintuitive but a freezer works harder in a cold environment than people expect.

Also check your DOD limits. Most LiFePO4 are rated to 80% usable, so your 200Ah is realistically 160Ah working capacity. Worth doing the maths on that figure rather than the headline number on the spec sheet.

@BayJason is right to nail down the actual wattage — stick a plug-in energy monitor on it for 24hrs before you commit to anything.