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

Running a small chest freezer off-grid is something I've been wrestling with lately, so hoping someone here can help me work this out before I commit to buying.

I've got a 200Ah 12V lithium (Fogstar Drift, so usable capacity is pretty much the full 200Ah) paired with a modest 400W of solar on the roof of my converted horsebox. Works brilliantly for most things, but I'm planning a longer trip up to Scotland in October and I'm thinking about adding a small chest freezer for the first time — probably something like a 60-70 litre unit.

My rough maths says a decent chest freezer pulls maybe 30-45W running, but obviously it's cycling on and off rather than drawing that constantly. Say it's actually averaging 1-1.5A per hour at 12V over an overnight stretch of roughly 10-12 hours — that's somewhere in the region of 10-18Ah consumed?

That sounds like it should be well within what the Fogstar can handle, especially since I don't want to draw below 20% anyway. But Scotland in October means overcast days, so solar recharge isn't guaranteed, and I'd rather not kill the battery cycling it hard every single night.

Has anyone actually measured their chest freezer draw overnight with a battery monitor? I've seen wildly different numbers thrown around depending on ambient temperature, how full the freezer is, and how often you open it.

Is 200Ah realistically enough, or am I going to struggle without a second battery in that scenario? Would love to hear from anyone who's done this properly rather than just going off spec sheets.

Hey @HarbourKev! Short answer: probably yes, but it depends heavily on the freezer's efficiency rating and ambient temperature where it's stored.

A decent small chest freezer (say 60-100L) typically pulls around 0.5-1kWh per 24 hours when running in a cool environment. Your 200Ah 12V lithium gives you roughly 2.4kWh usable (assuming 100% DoD, though I'd recommend staying above 20%). So overnight you're looking at using maybe 0.5-0.7kWh — well within budget.

The killer detail is compressor startup surge — make sure your inverter handles that peak draw comfortably.

What's the freezer model? If you can share it, I can give you a much more precise answer. Also worth checking whether it's stored indoors or outside, as ambient temperature massively affects runtime consumption. Summer in a hot shed versus a cool utility room makes a huge difference!

Good shout from @CraigThompson on efficiency ratings. One thing worth adding: chest freezers are actually ideal for off-grid use because the cold air doesn't fall out when opened, meaning the compressor cycles less frequently.

Practically speaking, a decent A+++ chest freezer in a cool garage will draw roughly 0.5–1kWh per 24 hours. At 12V that's 40–83Ah daily. Your 200Ah Fogstar gives you ~180Ah usable (assuming 90% DoD), so you're looking at 2+ nights realistically.

Where people get caught out is summer ambient temps — stick it somewhere shaded. I run a 100L chest freezer off a similar setup in my garden office and it's been solid all year.

Worth measuring the actual wattage with a Shelly plug or similar energy monitor before going fully off-grid with it. Real-world figures beat spec sheets every time.

What nobody's mentioned yet: duty cycle matters more than the nameplate wattage. A freezer doesn't run continuously — compressor kicks in maybe 20-40% of the time depending on ambient temp and how full it is.

Run it for a week and check actual consumption with a proper battery monitor (Victron BMV-712 is what I use on the boat). Guessing from specs is a fool's errand.

One thing that'll kill your margins: opening it repeatedly. On a boat or van that's unavoidable, but if it's a shepherd's hut situation where you're disciplined about access, you'll do considerably better than any calculation suggests.

200Ah usable (assuming you're not taking a Fogstar below 20%) should be fine for most small chest freezers overnight. Just don't run much else simultaneously.

Good timing on this thread — I've been running a Shoreline 60L chest freezer on the boat for two seasons now, so can offer real-world numbers rather than theory.

My setup is similar to yours and overnight I typically lose 15-25Ah depending on how warm the engine room gets. Summer's the killer, obviously.

The thing nobody's flagged yet: pre-cooling matters enormously. If you're transitioning from mains to off-grid, get that freezer down to temperature on shore power first. Starting the thermal battle from scratch hammers your battery far harder than maintaining an already-cold box.

Your 200Ah Fogstar should handle it comfortably, but I'd strongly suggest wiring a Victron battery protect or similar so you don't accidentally discharge below 20% if you've had a poor solar day. That's the scenario that bites you.