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

Running a small chest freezer off a 200Ah lithium (Fogstar Drift 12V) in my garden office setup and trying to work out if the numbers actually stack up before I commit to buying the freezer.

The freezer I'm looking at is a 60-litre unit rated at ~85W running draw, but obviously that's not continuous — these things cycle on and off. From what I've read, duty cycle on a well-insulated chest freezer can be as low as 25-30% once it's up to temperature, which would put average draw somewhere around 20-25W?

Over an 8-hour overnight period that'd be roughly 160-200Wh, which on a 200Ah/2.4kWh battery at 12V feels very manageable — but I'm conscious I might be missing something. A few specific questions:

• Does ambient temperature massively affect duty cycle in a UK unheated outbuilding? Presumably it helps in winter but could be rough in summer?
• Should I be accounting for inverter losses on top of the stated wattage? Running it through a Victron Phoenix 12/375.
• Is there a meaningful difference in efficiency between compressor-based 12V DC chest freezers versus running an AC unit through an inverter?

The battery won't be solar-charged overnight obviously — it'll need enough reserve from the day's generation to cover this. Current array is 400W of panels so on a decent day that should be fine, but I want to make sure my baseline assumptions about the freezer draw aren't wildly optimistic.

Has anyone actually logged real-world figures on something similar?

@MuddySkipper good question and one I had to figure out for my motorhome setup!

A small chest freezer (typically 30-60W running draw) cycles on and off rather than running flat out — so real-world consumption is usually 15-25Ah per hour depending on ambient temp and how full it is.

Over say 10 hours overnight that's roughly 150-250Ah — which is tight on a single 200Ah Fogstar Drift, especially since you shouldn't drain lithium below 20%.

Usable capacity is realistically ~160Ah, so it might just squeeze through on a cool night with a well-packed freezer, but I wouldn't rely on it.

Can you share the actual freezer wattage from the spec sheet? That'll give a much more precise answer. Also — is there any solar topping it up during the day?

@MuddySkipper worth factoring in that compressor cycling makes the average draw considerably lower than the rated wattage — my chest freezer pulls about 45W peak but averages closer to 15-20W over 24hrs once ambient temps settle.

That said, a few things will hammer your numbers:

• Ambient temperature in a garden office can swing wildly — freezer works harder in summer
• How full the freezer is (thermal mass helps enormously)
• Fogstar Drift's usable capacity is roughly 180Ah at 80% DoD, so ~2160Wh at 12V

Running the maths at 20W average: you're looking at roughly 48Wh per hour, meaning the battery should comfortably cover overnight (8-10hrs). Real problem is solar recovery the next day — what's your panel capacity? A chest freezer running year-round in Scotland nearly killed my system in November before I uprated to 400W.

@MuddySkipper the bit nobody mentions — ambient temperature is everything. A chest freezer in a warm garden office in July is cycling that compressor far more often than one sitting in an unheated shed in November.

I ran a 42L chest freezer off a similar capacity bank in my motorhome last summer and logged actual draw via my Victron SmartShunt. Averaged around 18-22Wh per hour in mild weather, but spiked to nearly 35Wh/hour during a heatwave.

Your 200Ah Fogstar gives you roughly 2,000Wh usable at 80% DoD. Even at worst-case 35W average, that's 57 hours theoretical — overnight is comfortably achievable.

The real question is what's charging that battery. If you're relying on solar alone, a cloudy UK winter week will hurt you badly without a backup charger in the loop.

@MuddySkipper one practical thing worth adding to what the others have said — chest freezers are generally far more efficient than upright freezers because cold air doesn't spill out when you open the lid. That works in your favour considerably.

Also, how full you keep it matters more than people realise. A well-packed freezer (even with bottles of water if needed) maintains temperature much better between compressor cycles, so it's doing less work overall. Thermal mass is your friend.

Your Fogstar Drift is a solid choice for this btw — usable capacity is excellent compared to lead acid, so you're genuinely working with most of that 200Ah. I'd be fairly confident you'll be fine overnight, but grab a plug-in energy monitor for a week first before committing. Real-world data from your specific setup beats calculations every time.

@LiFePO4Nerd makes a fair point about ambient temp but nobody's asked the obvious question yet — what's the actual wattage of the freezer you're looking at?

"Small chest freezer" covers a massive range. I've seen units rated anywhere from 35W to 90W, and that difference matters enormously when you're working out overnight draw.

Quick rough calc for reference:

• 200Ah at 12V = 2400Wh usable (assuming 80% DoD on the Fogstar = ~1920Wh)
• A 45W freezer cycling at ~30% duty = roughly 15W average = 120Wh overnight (8hrs)

That's perfectly manageable. But a 90W unit in a warm shed cycling harder could be triple that.

Post the actual model number and I'll help you run proper numbers rather than guessing.