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

Got a Fogstar Drift 200Ah sitting in my static caravan doing emergency backup duty, and I'm wondering if it'll cope with running my little Igenix 60L chest freezer through the night without me waking up to a puddle and very sad fish fingers.

The freezer pulls about 35W running, but I know these things cycle on and off rather than running constantly — from what I've read the compressor kicks in maybe 20-30% of the time depending on ambient temperature, so actual consumption might be somewhere around 150-200Wh over 8 hours? That sounds like the 200Ah (at 12V = 2,400Wh theoretical) should laugh at it, but I've learned never to trust theoretical numbers after my inverter incident of 2023 (we don't talk about that).

My concerns are:

• Inverter efficiency losses — I'm running it through a cheap 300W pure sine unit, so there'll be some overhead
• Compressor startup surge — will a 200Ah LiFePO4 handle the inrush without the BMS throwing a wobbly?
• Temperature — the caravan can get properly cold overnight, does that affect the battery's output meaningfully?

Has anyone actually done this rather than just done the maths on a napkin? Real-world numbers would be enormously reassuring before I commit to leaving it unattended.

Depends a lot on ambient temps but a 60L chest freezer is typically pulling 30-60W average (compressor cycles, doesn't run constantly).

Over say 10 hours that's maybe 300-600Wh. A 200Ah Fogstar Drift at 12V gives you roughly 2400Wh usable — so on paper you've got headroom.

Practical caveat though: don't drain it below 20% if you want longevity from the cells. Still leaves you plenty.

Bigger concern is whether you've got enough solar/charging to top it back up next day. I run a similar setup in my place and recovery time catches people out more than the overnight draw itself.

Worth sticking a basic energy monitor on it for a few nights first — see what the actual consumption looks like before relying on it for food safety.

@LiFePO4Fan has the wattage about right. Do the maths — at 45W average over 8 hours that's 360Wh, which on a 200Ah/2.56kWh Fogstar is roughly 14% of capacity. Easily manageable.

Real caveats though:

• Ambient temp matters massively. Freezer works harder in a warm caravan in summer
• Only use down to ~20% SOC on LiFePO4, so your usable window is ~2kWh
• Check what Igenix quotes for annual kWh and divide by 8,760 — gives you a realistic average draw

I ran a similar-sized chest freezer on my boat with a 100Ah Fogstar Drift for short stints and it was fine. 200Ah in a static with presumably some solar top-up during the day? You'll be absolutely fine overnight. Don't overthink it.

@RayWatson81 has the energy maths covered, so I'll add the practical caveat: that Fogstar Drift's usable capacity depends heavily on your discharge rate and the BMS cut-off settings. At 45W average load you're pulling roughly 3.7A from a 12V bank — well within comfortable territory for LiFePO4, so no de-rating concerns there.

What will catch you out is ambient temperature in the caravan. My garden office setup sees the same issue — on cold nights the freezer compressor barely cycles because the ambient is already cold, dropping average draw significantly. Conversely, a warm summer caravan could push that average toward 60W+.

Worth fitting a simple inline energy meter (Bayite or similar, £12 on Amazon) for a few nights to get your actual consumption before relying on it for anything critical. Real data beats estimates every time.

Good shout from all three of you. One thing nobody's flagged yet: startup surge. That Igenix compressor will spike 3-5x its running wattage on each cycle start. The Fogstar Drift handles this fine — its BMS is fairly robust — but if you're daisy-chaining it through an inverter, make sure you're not running something undersized that'll trip on inrush current.

On the narrowboat I ran a similar setup last summer; the freezer behaved itself all night but my cheap inverter kept nuisance-tripping until I swapped it for a Victron Phoenix 375VA. Made all the difference.

Also worth sticking a plug-in energy monitor on the freezer for a few days first — actual measured consumption beats estimated figures every time, and caravan ambient temps vary wildly depending on where you're sited.