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

Running a small chest freezer overnight is something I've been puzzling over for my emergency backup setup. Got a 200Ah lithium (Fogstar Drift 12V) that I'm hoping to press into service if the grid goes down, but I can't quite work out whether the maths stack up.

The freezer in question is a small Lec 100-litre chest freezer — manufacturers quote it at around 0.5kWh per 24 hours, which sounds promising on paper. That would suggest roughly 0.25kWh overnight (call it 8 hours), and a 200Ah lithium at 12V gives you around 2.4kWh usable (assuming 80% DoD). So theoretically there's bags of headroom?

But here's where I start second-guessing myself:

• The compressor start surge — does this cause problems with a standard inverter, or should I be looking at something with a soft-start feature?
• Ambient temperature matters, right? My garage in winter can drop to near freezing — does that affect how often the compressor cycles, or actually reduce the load since it's working less hard?
• Those manufacturer energy figures always seem optimistic. Anyone got real-world data from running a chest freezer off-grid?

I've got a Victron MultiPlus 12/1200 lined up as the inverter, which I think handles surge loads reasonably well, but I've not actually wired it up and tested it yet.

Essentially I want to know whether this is a solid plan or whether I'm being naively optimistic before I commit to this as my primary food-preservation strategy during a prolonged outage. Anyone done something similar?

@SolarRachel depends almost entirely on the freezer. A decent chest freezer (they're more efficient than uprights) typically pulls 100-150Wh per 24hrs once it's already cold and ambient temps aren't crazy. So overnight — say 8-10hrs — you're looking at maybe 40-70Wh if it's not working hard.

Your 200Ah Fogstar at 12V is 2.4kWh usable (assuming ~85% DoD). So in theory, yes, easily. But that's best-case.

Where it gets sketchy:

• If the freezer starts warm, compressor runs constantly for hours
• UK summer ambient temps kill efficiency
• Starting surge can be 3-5x running watts

What's the actual freezer model? The nameplate wattage is pretty much useless — real-world consumption varies wildly. I'd stick a cheap energy monitor on it for 48hrs before trusting any calculations.

@ExPostie is right about freezer efficiency, but there's another variable worth flagging — ambient temperature.

In summer, a chest freezer works considerably harder than in winter. On my narrowboat last August, my small 60L chest unit was pulling nearly double its rated consumption because the engine bay gets warm.

With a Fogstar Drift 200Ah you've got roughly 2.4kWh usable (assuming Fogstar's sensible 100% DoD rating, though I'd keep it to 80-90% for longevity). A reasonably efficient chest freezer might average 50-80W, so overnight (say 10 hours) that's 500-800Wh — well within budget.

Key things to check:

• Starting surge — ensure your inverter handles it
• Thermostat cycling frequency in your environment
• Pre-cool the freezer on mains before switching over

Should be absolutely fine for overnight, but monitor it the first time with a plug-in energy meter.

Quick rule of thumb from my static caravan setup — a well-stocked freezer holds temp better than an empty one. Thermal mass is your friend.

So the answer to "will 200Ah run it overnight" is partly "what did you put in the freezer?" 😄

Seriously though, I've run a small chest freezer off a 100

Worth adding — starting current (inrush) on compressors can spike quite high momentarily. Make sure your Fogstar BMS and any inverter you're running it through can handle that without tripping. Some smaller inverters get funny about it.

Also worth thinking about what usable capacity actually is. A 200Ah Fogstar Drift gives you roughly 180-190Ah usable which is generous, but factor in inverter losses if you're running 230V. A 12V DC chest freezer (they exist, Dometic etc.) cuts that inefficiency out entirely — something I wish I'd considered before buying my setup.

Overnight is probably fine in most cases but I'd log actual consumption with a battery monitor first if you can. Victron BMV-712 shows patterns clearly. Surprises me how much variance there is between freezer models even with similar stated wattage.

Good point from @LiFePO4Fan on the inrush — worth checking your inverter's surge rating too, not just the BMS.

From my own experience running a small chest freezer off a similar setup on the boat: the compressor duty cycle matters enormously. Mine pulls about 80-90W when running but only kicks in maybe 30-40% of the time once the freezer is up to temperature. That works out roughly 1-1.5kWh overnight — well within what a 200Ah Fogstar can deliver if you're staying above the recommended 20% DoD.

The key variable nobody's mentioned yet is your inverter efficiency. A cheap inverter sitting idle still draws parasitic current all night. Worth factoring that into your calculations, or look at whether the freezer can run directly from 12V DC if it has that option.