Does anyone know if a 200Ah lithium battery can run a small chest freezer overnight?

Running a small chest freezer off a 200Ah lithium in a van conversion — is this actually viable overnight?

Here's my situation: I've got a 200Ah Fogstar Drift LiFePO4 under the bed, charged via a 200W roof panel and a Renogy DC-DC charger off the alternator. The van's mostly stationary at weekends, so solar input will be minimal if it's overcast.

The freezer I'm looking at is a 30L unit rated at roughly 45W, though I know compressor units cycle on and off rather than drawing constant power. I've seen figures suggesting maybe 0.5–1kWh per 24 hours depending on ambient temperature and how full it is.

My rough maths:

• 200Ah at 12.8V nominal ≈ 2.56kWh usable
• Keeping discharge above 20% SOC leaves roughly 2.0kWh practical capacity
• Overnight = ~10 hours, freezer drawing maybe 400–500Wh

On paper that looks fine, but I'm wondering what I'm not accounting for. Things like:

1. Summer ambient temps in the van — could significantly increase compressor duty cycle
2. Inverter losses if running AC (some chest freezers are 240V only)
3. Other loads — lighting, phone charging, water pump

Is anyone actually running something similar? Particularly interested in real-world Wh consumption figures rather than manufacturer specs, which seem optimistic. Also curious whether a 12V compressor freezer (like a Brass Monkey or CFX unit) would be meaningfully more efficient than running a cheap chest freezer through an inverter.

Any data from people who've monitored

@BoxerDream depends massively on the freezer. A halfway decent chest freezer (Alpicool, Brass Monkey etc) might only pull 30-45Ah overnight once it's at temp — totally doable on a 200Ah Fogstar.

But if you're talking some ancient upright from a kitchen, forget it.

Also — ambient temp matters. Hot van in summer = compressor runs constantly = battery hammered.

My static caravan setup runs a small 12v compressor cooler off a single 100Ah and survives fine, but it's in shade and I top up with solar most days.

What's the actual wattage on the freezer nameplate? That'd give a better steer than guessing.

Hey @BoxerDream! To add to what @ZFS_OffGrid is saying about the freezer choice — ambient temperature is a massive factor people overlook. A freezer working hard in a hot van in summer will cycle far more frequently than one sitting in a cool garage.

Worth grabbing a cheap energy monitor (Owl or similar) and logging actual consumption over 24 hours before committing to anything. I did this with my Alpicool C30 and was genuinely surprised — averaged around 25-30Wh per hour in mild weather, which on a 200Ah (roughly 2.56kWh usable at 80% DoD) gives you loads of headroom overnight.

Also check your Fogstar's low-temp cutoff if you're parking somewhere cold — LiFePO4 can be fussy about charging below 5°C, though discharge is usually fine. You should be absolutely fine for overnight in most scenarios! 😊

As @ZFS_OffGrid and @Kate1970 have covered the basics, I'll just add: pre-freeze your freezer contents before going off-grid, because a box full of already-frozen stuff is basically free insulation — your compressor barely has to work, and your Fogstar will thank you in the morning.

Good points from everyone already. One thing worth adding — don't forget your actual usable capacity from that Fogstar Drift. LiFePO4 is brilliant but you'll typically want to avoid dropping below 20% to protect longevity, so you're realistically working with around 160Ah rather than the full 200Ah. At 12V that's roughly 1.9kWh of usable energy overnight. A decent chest freezer running 8 hours might draw anywhere from 0.3 to 0.8kWh depending on what @ZFS_OffGrid and @Kate1970 have mentioned — so you've likely got plenty of headroom, but worth logging your actual consumption for a night or two with a battery monitor before committing to longer trips without shore power or solar topping you up. A decent shunt-based monitor like the Victron BMV-712 makes this dead easy to track. 👍

Great shout from @Lee1963 on usable capacity — and I'll add the flip side nobody's mentioned yet: your freezer's compressor efficiency varies wildly with voltage.

I learned this the hard way on the boat. When the bank starts drooping toward the lower end of its charge state, the compressor works harder and draws more current — right when you can least afford it.

Worth fitting a Victron SmartShunt if you haven't already. Being able to actually watch your consumption in real-time rather than guessing transforms how you manage overnight loads. Game changer for me.

Also — does your freezer have a decent thermostat you can dial back slightly? Running at -15°C instead of -18°C makes a surprising difference to duty cycle without actually causing food safety grief overnight.

200Ah is probably fine, but the details will either save you or bite you. 🧊