Anyone know if a 200Ah lithium battery is enough to run a small chest freezer overnight?

Running a small chest freezer in my garden office off a 200Ah Fogstar Drift lithium — wondering if I'm setting myself up for a midnight meltdown (of the frozen peas variety).

The freezer is a Cookology 60L chest freezer, rated at about 85W but obviously it's not running continuously — duty cycle seems to be roughly 30-40% from what I've read, so maybe ~200-280Wh overnight across 8 hours?

My rough maths:

• 200Ah at 12V = 2,400Wh theoretical
• Usable at 80% DoD = ~1,920Wh
• Freezer overnight = probably 250Wh-ish?

On paper that looks miles comfortable, but I'm paranoid I'm missing something obvious. A few specific worries:

1. Ambient temperature — garden office gets properly cold in winter, does that affect the compressor duty cycle weirdly (more or less runtime)?
2. Startup surge — my Victron SmartShunt occasionally throws a wobble when the compressor kicks in; is 200Ah enough to handle that without the BMS getting stroppy?
3. Am I being an idiot and the real consumption is actually much higher than my back-of-envelope maths suggests?

Has anyone actually measured their chest freezer draw with a Shelly plug or similar rather than just theorising like I clearly am? Would love some real-world numbers before I commit to leaving it unattended overnight rather than just plugging it into the mains like a sensible person.

@QuietHiker the Cookoo (assuming it's one of those ~60-100W rated chest freezers) won't run the compressor flat out all night — duty cycle is your friend here. Realistically you're looking at maybe 30-40% on-time once it's pre-chilled, so call it 150-250Wh overnight depending on ambient temp.

Your 200Ah Fogstar Drift at 12V = 2400Wh nominal, but you want to stay above 20% SOC on lithium, so ~1920Wh usable. You're absolutely fine on capacity alone.

The gotcha is surge current when the compressor kicks in — check what your BMS peak rating is. Fogstar Drift handles it well in my experience running a similar setup in my tiny house, but worth confirming your inverter isn't undersized.

What's your inverter situation?

@QuietHiker what's your actual overnight hours looking like — 8 hours, 10 hours? That makes a big difference to the maths.

Also worth checking: is your Fogstar Drift a 12V or 24V setup? And what inverter are you running it through? Inverter efficiency losses can quietly eat into your usable capacity more than people expect.

The other thing I'd want to know is whether the garden office gets cold overnight — a freezer in a cool environment cycles the compressor far less frequently, which could actually make your 200Ah quite comfortable. Conversely, if it's sitting in a warm space during summer, duty cycle goes up noticeably.

Have you got a way to monitor actual draw? Something like a Victron BMV or a basic plug-in energy monitor on the output side would give you real numbers rather than guesswork.

@QuietHiker running a similar setup in my garden office — chest freezer on a Fogstar Drift 200Ah.

Real-world overnight (say 10hrs) the compressor duty cycle is your friend. Mine barely pulls 150-200Wh across a full night once it's already cold. The key bit: pre-cool it during the day when your panels are doing the work, then it's just maintaining temp overnight.

200Ah at 12V is 2.4kWh usable (ish, assuming ~80% DoD) — more than enough headroom unless it's a scorching summer night or the freezer's half empty.

One thing worth checking: what's your inverter? A cheap pure sine can have high idle draw that'll quietly eat your reserves more than the freezer will.

Don't forget a well-stuffed freezer is basically a self-insulating brick — mine barely blinks overnight on a 200Ah Victron setup once it's pre-chilled properly.