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

Running a small chest freezer off-grid is something I'm trying to get my head around for the shepherd's hut, so this is timely for me too.

I've got a 200Ah LiFePO4 (Fogstar Drift) and I'm trying to work out whether it'll realistically carry a small chest freezer — something like a 60-70 litre unit — through an overnight stretch of say 10-12 hours without solar input.

The maths looks promising on paper. A decent chest freezer in a cool environment might average 30-50W once it's up to temperature, which over 12 hours is roughly 360-600Wh. A 200Ah battery at 12V gives you around 2.4kWh usable (assuming you're not going below 20% SoC), so in theory there's headroom.

But I'm suspicious of those average wattage figures. A few things I'm unsure about:

• Ambient temperature — the hut can get warm in summer, which will hammer the duty cycle
• Inverter losses — I'd be running it through a pure sine inverter, probably adding 10-15% overhead
• Initial pull-down — if the freezer isn't pre-cooled, the compressor will run almost continuously for the first few hours

Has anyone actually logged real consumption data on a chest freezer overnight? I'm wondering whether a dedicated 12V compressor unit (like an Alpicool or similar) would be far more efficient than a mains chest freezer on an inverter.

Also curious whether anyone's used a smart plug with energy monitoring to get accurate figures before committing to a setup.

Ran a small chest freezer on my narrowboat for two summers — 200Ah is fine overnight, but only because a chest freezer cycles on maybe 30-40% duty cycle once it's pre-chilled, so you're realistically drawing 2-3A average rather than the peak figure on the label.

Key thing @LutonCamper: pre-cool it on mains before you go off-grid — trying to pull a warm freezer down to temp on battery alone will absolutely murder your SOC before midnight.

Good shout from @FormerMachanic43 on the chest freezer efficiency point. The bit people miss is ambient temperature — in a shepherd's hut that's not well-insulated, a freezer working hard in summer can easily double its duty cycle. I've run a small Liebherr chest freezer in my hut and monitored it with a Victron BMV-712; actual draw averaged around 35-45Wh per hour once you account for compressor cycles.

With a Fogstar Drift 200Ah at 51.2V nominal, you're looking at roughly 10.24kWh usable (allowing 80% DoD) — more than enough overnight, but factor in your other loads. A single 200W panel won't recover that fast in winter either, so watch your SoC trending downward across consecutive overcast days.

Done exactly this in my shepherd's hut — Fogstar Drift 200Ah paired with a Victron SmartShunt so you can actually see what the freezer's pulling rather than guessing.

Key thing nobody's mentioned: lid gasket condition matters enormously. A dodgy seal on a chest freezer will have your compressor cycling constantly and your 200Ah looking very sorry for itself by 3am.

Also worth checking if your freezer has an ECO mode — some of the smaller units (Subcold, Brass Monkey etc.) do, and it makes a measurable difference overnight.

Rule of thumb: a decent small chest freezer in good nick will use roughly 0.3–0.5kWh per 24hrs, so your 200Ah (at ~2.56kWh usable to 80% DoD) should handle it with capacity to spare.

Good timing — I've got a shepherd's hut setup myself so this is directly relevant.

One thing nobody's mentioned yet: duty cycle varies massively depending on how full the freezer is. A packed freezer holds temperature far better than a half-empty one, so it cycles the compressor less. If you're only running it partially loaded, chuck some frozen water bottles in to fill the space.

Also worth checking the startup (inrush) current on whatever freezer you pick. Some small compressors pull 3-4x rated watts for a second on startup. Your Fogstar Drift can handle it, but your inverter needs to be rated accordingly — caught people out before.

@MarineGeoff's point on the SmartShunt is solid. You really do need to see what's happening rather than guess.

What inverter are you running with it?

@MarineGeoff good to hear the Fogstar Drift handles this in practice — I've got one running my garden office and it's been solid.

The thing I'd add: freezer starting current catches people out. The compressor startup surge can trip cheap inverters even if the running wattage looks fine on paper. Worth checking your inverter's peak surge rating against the freezer's LRA (locked rotor amps) — usually on the data plate.

For reference, my setup runs a small bar fridge overnight no bother on a similar capacity battery, but a chest freezer will cycle more frequently depending on how full it is. A fuller freezer is actually more efficient — the thermal mass helps.

What inverter are you planning to use? That matters as much as the battery capacity here.

Been running a small chest freezer on my narrowboat for a couple of seasons now, so can add something practical here.

The bit people overlook is ambient temperature. A freezer working hard in a warm shepherd's hut in summer will pull considerably more than the nameplate suggests — I've seen mine spike to 80W+ during compressor cycles on hot days. Worth logging actual consumption with a smart meter plug before committing to battery sizing.

Also worth noting: 200Ah LiFePO4 gives you roughly 160Ah usable if you're being sensible with it (keeping above 10-20% SoC to protect cycle life). Whether that's enough overnight really depends on your freezer's duty cycle and ambient temps.

What freezer model are you looking at? Some of the 12V compressor units like Brass Monkey or Dometic are noticeably more efficient than a converted mains chest freezer.