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

Running the numbers on this has got me a bit turned around, so hoping someone with more practical experience can help clarify.

My setup is a static caravan with a 200Ah 12V LiFePO4 (Fogstar Drift), paired with 400W of solar and a Victron SmartSolar MPPT. Works brilliantly for most things, but I'm considering adding a small chest freezer — probably something in the 60–100 litre range — primarily as an emergency backup food store when grid power goes down.

From what I've read, a small chest freezer typically draws somewhere between 80–150W when the compressor is running, but the duty cycle is the variable I can't pin down. Some sources suggest it's only running perhaps 25–35% of the time once it's at temperature, which would put overnight consumption (say, 10 hours) somewhere around 200–375Wh. That sounds manageable on a 200Ah battery, especially if I'm not drawing the full usable capacity.

However, I'm conscious that:

• Overnight means no solar replenishment
• I'd want to keep SoC above 20% to protect the cells
• Startup surge current on compressors can be significant

So realistically, am I looking at perhaps 160Ah of usable capacity (80% of 200Ah), which at 12V gives around 1920Wh — and whether that's comfortably sufficient, or whether real-world freezer behaviour makes this tighter than it looks on paper?

Has anyone actually monitored their freezer draw with a proper energy meter overnight? Particularly interested in whether ambient temperature in an uninsulated caravan makes the duty cycle significantly worse in summer.

@Nessa depends entirely on the freezer's actual draw. Chest freezers are cyclic — mine pulls ~2.5A when compressor's running but sits idle maybe 60-70% of the time in cool ambient. So real-world average is often 0.7–1.2A at 12V.

Over 10hrs that's roughly 7–12Ah. Even accounting for inverter losses (assume ~10-15%), you're nowhere near stressing a 200Ah Fogstar.

The gotcha: ambient temp matters massively. Warm summer nights = compressor runs longer. Also don't forget LiFePO4 usable capacity is typically 80% if you're being sensible, so your real headroom is ~160Ah.

Grab a cheap energy monitor (Owl or similar) and measure the actual freezer draw for 24hrs before committing. Don't guess — measure.

@Nessa to add to what @OakSpirit said about the cyclic nature — that's the key bit people often miss. Your 200Ah Fogstar gives you a usable 180Ah or so (LiFePO4 is brilliant for this), but the freezer won't be drawing constantly.

A typical small chest freezer might run its compressor 30-40% of the time overnight, so your actual consumption could be closer to 15-25Ah over 8 hours rather than the worst-case figure.

Realistically you should be absolutely fine, provided you're not starting from a depleted battery and you've got decent solar topping it back up the following day. Worth plugging a plug-in energy monitor (Owl or similar) onto it for a few days first to get your actual figures rather than guessing from the spec sheet. That'll tell you exactly what you're dealing with.

Really curious about this one as I'm trying to work out something similar for my garden office setup.

@OakSpirit and @YorkshireSolar have covered the cyclic draw well — but one thing I keep wondering: does the ambient temperature of where the freezer's sitting make a significant difference to how often the compressor kicks in? I'd imagine a freezer in an uninsulated caravan in, say, a cold Scottish winter runs very differently to one baking in a summer heatwave.

Also @Nessa — what's your actual usable capacity on that Fogstar? I've seen people assume 200Ah is 200Ah, but with LiFePO4 you're typically working to about 80-90% to preserve cycle life. Worth factoring that into your overnight calculation before you commit.

Done this exact thing with my garden office setup — chest freezer on a 200Ah LiFePO4 overnight is very doable.

Practical numbers: a decent small chest freezer (say 60-100L) typically averages 15-25Wh per hour once it's already cold, so roughly 120-200Wh overnight (8hrs). That's well within your Fogstar's usable capacity (~2kWh at 80% DoD).

Key things that'll shift those numbers:

• Ambient temp — colder outside = compressor runs less
• How full it is — fuller freezer holds temp better
• Pre-cooling on mains before switching over

@HollyGazer for garden office use I'd still recommend a Victron SmartShunt so you can actually see consumption in real-time rather than guessing. Made a big difference to my confidence in the system.

@Nessa you should be fine, but measure your specific freezer with a plug-in energy monitor first — models vary quite a bit.