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

Got a Fogstar 200Ah LiFePO4 sitting in my static and I'm trying to work out if it's enough to keep a small chest freezer running through the night without solar input.

The freezer is a Shoreline 60L — draws about 85W when the compressor kicks in but it's obviously not running constantly. I've seen figures suggesting maybe 0.3–0.5kWh per 24hrs for a well-insulated chest freezer, but I'm not confident in those numbers for overnight use specifically (say 10pm to 8am).

My rough maths:

• 200Ah at 12V = 2.4kWh usable
• With LiFePO4 I'm comfortable pulling down to about 20%, so roughly 1.9kWh available
• Freezer overnight maybe 0.2–0.25kWh?

On paper it looks fine but I'm worried I'm missing something — ambient temperature in the van/caravan affecting compressor duty cycle, inverter losses, etc.

Anyone actually run a setup like this? I've got a Victron 500W inverter in the mix so there'll be some conversion losses on top.

Would be running this on the narrowboat too eventually where overnight solar obviously isn't an option in winter, so want to get the maths right before I commit to anything. Is 200Ah actually sufficient or should I be looking at a second battery?

@CaddyDream the maths is pretty workable actually. A Shoreline 60 typically draws around 35-45W when the compressor's running, but it cycles — usually around 30-40% duty cycle once it's up to temp. So you're realistically looking at maybe 15-18W average overnight.

Eight hours = roughly 120-145Wh drawn from the battery.

Your 200Ah Fogstar at 12V = 2400Wh nominal, and LiFePO4 is happy down to about 80% DoD usably, so you've got ~1920Wh to play with.

Short answer: yes, easily. The freezer shouldn't touch more than 10% of your usable capacity overnight.

One caveat — if it's a warm night or the freezer isn't pre-cooled, the compressor runs harder. Worth chucking a basic current clamp on it first to see your actual duty cycle rather than trusting spec sheets.

Don't forget LiFePO4 only likes you using ~80% of that 200Ah before it starts sulking, so you're really working with 160Ah — still plenty for one night, but if your static gets warm the compressor cycles more and your margins shrink faster than my patience at a B&Q returns desk.

@SaltyMechanic raises the right point on usable capacity, though with a quality Fogstar cell the BMS will typically cut out around 10-20% SOC, so 160Ah is a reasonable working figure at 12V — that's roughly 1.92kWh available.

The variable nobody's mentioned yet is ambient temperature. A chest freezer in a static during a cold UK night is going to cycle far less frequently than in summer — compressor might only run 20-30% duty cycle versus 50%+ in July. That dramatically changes your overnight consumption figure.

Worth checking if your Shoreline has an actual power meter on it or whether you're going off spec sheet numbers. I ran a similar setup with a Victron SmartShunt and found my actual measured draw was noticeably lower than the rated figures suggested.

If you've got a Victron BMV or similar, log a full night's data before committing to anything permanent.

@SaltyMechanic and @CrafterConvert have covered the usable capacity side well.

One thing nobody's mentioned — ambient temperature matters a lot. A chest freezer in a warm static caravan in summer will cycle far more frequently than one sitting in an unheated outbuilding in October. Your real-world draw could swing quite a bit either way.

Also worth checking: does the Shoreline 60 have a high starting surge? Some compressors pull 3-4x running watts at startup. Worth confirming your Fogstar's BMS can handle that without tripping.

I ran a similar setup last year — 200Ah Fogstar, small freezer, no solar overnight. Made it through fine in autumn but summer was marginal. I'd keep a Victron BMV on it so you can actually see where you're landing rather than guessing.

Short answer: probably fine, but monitor it for a few nights before relying on it.