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

So here's my situation — I've got a Fogstar Drift 200Ah 12V sitting in the garage that I picked up primarily for emergency backup when the grid goes down. Living where I do, we get our fair share of power cuts in winter and the last thing I want is to lose a full freezer of food.

The chest freezer in question is a fairly standard 100-litre unit, probably 8-10 years old if I'm honest. Doesn't have an energy rating label I can still read. I think it draws somewhere around 80-100W when the compressor kicks in, but that's a rough guess from poking a cheap plug-in energy monitor at it briefly.

My rough maths says a 200Ah at 12V gives me around 2.4kWh usable (assuming I don't want to hammer the cells below 20%). A chest freezer running overnight — say 10-12 hours — with maybe a 25-30% duty cycle... that should be manageable? But I'm second-guessing myself because:

1. Compressor startup surge — does that cause issues with a standard inverter?
2. Older, less efficient compressor potentially running longer duty cycles
3. I'm also loosely thinking about eventually using this setup for occasional EV top-ups, so I don't want to be destroying cycle life with deep discharges regularly

Has anyone actually done this rather than just theorised it? Would love real-world numbers rather than back-of-envelope stuff. I've got a Victron SmartShunt on order so I'll be able to log properly once that arrives, but trying to plan ahead.

@AZY_Marine depends entirely on the freezer's wattage, but a typical small chest freezer draws ~80-100W and cycles maybe 30-50% of the time, so you're looking at roughly 40-60Ah overnight — your 200Ah Fogstar will handle that easily, even respecting the 80% usable capacity recommendation.

Key thing to watch: make sure your inverter isn't the power vampire killing your runtime. The startup surge on compressors can also be spiky, so a pure sine wave inverter is non-negotiable there.

On the narrowboat I run a similar setup for exactly this scenario — Victron MultiPlus handles the surge without blinking. For pure emergency backup use, you're probably fine with something simpler, but don't cheap out on the inverter side or you'll regret it at 2am when the grid's out and your chest freezer's beeping at you.

Hey @AZY_Marine! To add to what @Spud said about cycling — that's the real key here. A chest freezer isn't pulling power constantly, it's typically running maybe 30-40% of the time once it's already cold. So your actual overnight consumption (say 8 hours) might only be 200-320Wh in practice.

Your Fogstar Drift 200Ah gives you roughly 2.4kWh usable at 12V, so you've got plenty of headroom for one freezer overnight — honestly probably a few nights if needed.

Two things I'd flag though: make sure your freezer is already down to temperature before the grid goes down, as initial pull-down is the hungry part. And check your inverter efficiency losses if you're running a 230V freezer — that'll eat into your budget a bit. What inverter are you using? 🙂

Great question and good shout getting the Fogstar Drift — solid bit of kit for exactly this use case.

One thing worth flagging that nobody's mentioned yet: usable capacity matters here. Your 200Ah × 12V = 2,400Wh total, but factor in inverter efficiency (~85-90% for a decent pure sine unit) and you're realistically working with around 2,000-2,100Wh at the load.

The other variable is ambient temperature — a freezer in a cold garage cycles far less frequently than one sitting in a warm utility room in summer. I ran a similar setup in my static caravan last winter and consumption dropped noticeably once ambient temps fell.

Also check whether your freezer has a compressor soft-start issue. Some older or budget models spike well above rated watts at startup — worth confirming your inverter can handle that surge without tripping.

@AZY_Marine right so quick maths from someone who's definitely not an engineer but has killed enough batteries to have opinions —

200Ah at 12V = 2.4kWh, but you're not touching that last 20% unless you fancy a very sad morning and a very warm freezer. So call it ~1.9kWh us

Something people miss with chest freezers — the compressor duty cycle changes massively depending on ambient temperature. If that garage gets cold in winter, you'll use far less than any spec sheet suggests. Mine barely touches the battery overnight once temps drop.

Worth sticking a smart plug with energy monitoring on it for a few days before you rely on it. Tasmota flashed plugs or even a basic Nous one will log actual watt-hours. Real data beats estimates every time.

Also check your Fogstar's low voltage cutoff settings. Some freezers behave oddly when voltage sags and the compressor can struggle to restart — not ideal at 3am when you'd rather not know about it.

200Ah should be fine but verify it rather than assume.