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

So I've been scratching my head over this one for a few weeks now. Got a Fogstar Drift 200Ah 12V sitting in my garden office setup, paired with a modest 400W of solar on the roof, and I'm wondering whether it could realistically carry a small chest freezer through the night without the panels doing anything.

The freezer in question is a Liebherr GT2132 — rated at about 90W but obviously it's not running flat-out continuously, duty cycle being what it is. I've seen figures suggesting maybe 30–40% duty cycle in a cool garage, so rough maths gives me something like:

• ~35W average draw
• 8 hours overnight = ~280Wh consumed
• 200Ah × 12V = 2,400Wh usable (assuming ~85% DoD on LiFePO4, so ~2,040Wh)

On paper it looks very comfortable, but that's assuming my duty cycle estimate isn't wildly optimistic and the inverter losses aren't eating me alive. Running it through a Victron Phoenix 12/500, which I believe idles at around 8–10W, so that's another 80-odd Wh to factor in over 8 hours.

Has anyone actually measured their chest freezer overnight draw with a clamp meter or an energy monitor? I've got a Shelly PM I could stick on it but wondered if anyone had real-world numbers before I bother wiring it up properly.

Also — does ambient temperature in a UK garden outbuilding through autumn/winter actually help the duty cycle much, or does the compressor compensate oddly and behave unpredictably?

Any lived experience appreciated!

@TracyAllen depends heavily on the freezer. Most chest freezers pull 80-150W but only cycle ~30-40% of the time, so real consumption is maybe 1-1.5kWh per 8hr night.

Your 200Ah at 12V is ~2.4kWh usable (assuming 100% DoD on the Drift, which is rated for it). So on paper you're fine, but:

• Ambient temp matters massively — warmer = compressor runs longer
• How full the freezer is (thermal mass helps)
• What else is drawing from the battery overnight

Running mine on a similar setup in a motorhome. A decent chest freezer overnight is doable but leaves little headroom. I'd measure actual draw with a clamp meter first — don't guess.

Your 400W solar should recover it fine by midday assuming decent weather.

@TracyAllen @CaddyProject is right about duty cycle, but here's the maths that'll actually help you:

Usable capacity on your Fogstar Drift at 80% DoD = 160Ah @ 12V = ~1,920Wh

A typical chest freezer doing 35% duty cycle at 120W averages roughly 42W continuous, so overnight (say 10 hours) that's 420Wh — well within your budget, leaving plenty for other loads.

The critical caveat: ambient temperature matters enormously. A poorly insulated freezer in a warm summer outbuilding could push duty cycle above 60%, doubling that draw.

Worth grabbing a Owl or similar energy monitor and logging actual consumption for 24 hours before committing. Run it off mains first.

My narrowboat setup runs a chest freezer on a similar battery bank without issue through most of the year. Winter solar recharge is where things get trickier, but that's a separate conversation.

@TracyAllen running almost exactly this setup in my Vivaro conversion — Fogstar Drift 200Ah paired with a small Waeco compressor fridge (similar draw characteristics to a chest freezer).

Real-world overnight figure: I lose roughly 40-55Ah across a 10-hour night, which on a 200Ah Fogstar (usable ~180Ah to keep above 10%) leaves comfortable headroom.

The variable nobody's mentioned yet is ambient temperature — a freezer working hard in a warm garden office will cycle far more aggressively than one in a cool environment. Mine sits in an uninsulated van, so summer nights are noticeably heavier draws.

Worth logging actual consumption with a Victron BMV-712 or similar shunt meter for a week rather than relying purely on calculated estimates. Manufacturers' wattage figures are often measured at optimistic ambient temps.

@TracyAllen my tiny house has been running a chest freezer off similar capacity for two years — the freezer's the most honest lodger I've ever had, costs about the same every night regardless of my feelings about it.

@TracyAllen one thing nobody's mentioned yet — ambient temperature matters enormously here. A chest freezer in a warm garden office in July is working far harder than one in an unheated space in winter. That directly affects duty cycle, sometimes doubling it.

Also worth checking: is the Fogstar Drift's BMS configured for low-temperature cutoff? If your office drops below ~5°C overnight, you could lose usable capacity at the worst possible moment.

400W solar is fine for recovery during daylight, but that's irrelevant to whether you survive the night. Run the freezer with a clamp meter for a full 24 hours and log actual consumption — guessing duty cycle from spec sheets is how people end up with warm food.

The 200Ah should be adequate, but margin depends entirely on your specific freezer model and installation conditions.