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

Running a small chest freezer overnight from a 200Ah lithium (Fogstar Drift, if it matters) in my static caravan — anyone actually done this, or am I about to have a very warm prawn situation?

Context: it's purely for emergency backup when the hook-up goes down, so it won't be a daily cycle. The freezer is a 60-litre Iceking, pulls around 90W when the compressor kicks in but obviously not running continuously.

A few things I'm genuinely unsure about:

• At 12V, 200Ah gives me roughly 2.4kWh usable (assuming 80% DoD) — is that maths even right, or have I done something embarrassing?
• How often does a small chest freezer actually cycle? I've seen everything from 20% to 50% duty cycle quoted online and that's a massive difference overnight
• Would a 1000W pure sine inverter be overkill, or does the compressor startup surge need it?

The caravan also has a bit of solar (2× 175W Renogy panels, Victron SmartSolar MPPT) so if there's any daylight it'll be topping up, but I'm planning for a worst-case cloudy scenario.

Basically: will the prawns survive, or should I just buy more ice?

@HeatherChild done exactly this in my motorhome last summer — chest freezer running overnight off a 200Ah Fogstar Drift, same battery actually.

The honest answer is: it depends entirely on the freezer. Mine pulls around 30–40Ah overnight once it's already cold, which a 200Ah handles comfortably (especially keeping above 80% DoD for longevity).

The killer detail nobody mentions — pre-cooling matters enormously. If your freezer is already at temperature when the sun goes down, the compressor barely touches the battery. If it's working hard to pull down temperature all night, you're in a different story.

What freezer is it? Some of those small chest units are surprisingly efficient. If you've got a clamp meter, chuck it on for one evening and see what you're actually dealing with before committing the prawns to their fate. 🦐

@HeatherChild small chest freezers typically draw 30–60Ah overnight once they've reached temperature, so your 200Ah Fogstar Drift should handle it with capacity to spare — assuming you're not starting with a warm box full of fresh prawns it's desperately trying to freeze from scratch.

Key things that'll make or break it:

• Ambient temperature (cold garage = freezer works less, happy days)
• How full it is (thermal mass is your friend)
• Your inverter efficiency — a cheap one will quietly eat 10–15% of your budget

Worth chucking a Victron SmartShunt on there so you can actually see what it's consuming rather than guessing. One night of data tells you more than a forum full of opinions, including this one.

@HeatherChild one thing worth flagging that @MarineGeoff and @MarineVicky haven't touched on — ambient temperature matters enormously here. A chest freezer in a static caravan on a warm August night will cycle far more frequently than one sitting in a cool outbuilding. My garden office setup sees my fridge load nearly double in summer compared to winter.

Also check your Fogstar Drift's low-temperature cutoff if nights are dropping near freezing — lithium BMS protection can disconnect unexpectedly and you'll wake up to exactly the warm prawn scenario you're dreading.

Practical suggestion: run a Victron SmartShunt for even one night on mains first to log actual Ah consumption before committing to overnight off-grid. Takes the guesswork out entirely. A 200Ah pack should be fine, but "should" doesn't save prawns.

What's the starting temp of the freezer when you plug it in? If it's already warm (like you've just bought it and it's been sitting in a shop), that initial pull-down is going to hammer the battery hard compared to just maintaining temperature overnight.

Also — static caravan specific thing here — is it insulated at all or just a thin-walled chest freezer sitting in an uninsulated space? Mine's in a utility cupboard and I noticed a big difference once I added some basic insulation around the caravan walls nearby.

One more thing: what's your charge source for the next morning? If you're solar-only and it's a cloudy UK autumn day you might be starting the following night already depleted. That's where I've come unstuck before.

@HeatherChild I've got a small Outwell chest freezer running off a 100Ah Drift in my van, so your 200Ah should be absolutely fine in normal circumstances. One thing nobody's mentioned yet — chest freezers are generally far more efficient than upright models because the cold air doesn't just fall out when you open the lid. That works in your favour here. Also worth checking whether your caravan has decent insulation around where the freezer sits; if it's up against a warm wall or in direct sun, the compressor will work harder than it needs to. I'd suggest grabbing a cheap plug-in energy monitor (Owl or similar) for a few nights to see your actual draw — takes the guesswork out completely. Your prawns should be absolutely fine! 🦐