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

Got a Fogstar Drift 200Ah sitting in the motorhome and I'm wondering if it'll keep a small chest freezer ticking over through the night without flattening itself — anyone actually done this or am I about to learn an expensive lesson?

Context: the freezer is a Subcold 35L, pulls around 45W when the compressor kicks in but obviously it's duty cycling so real-world draw is probably closer to 15-20W average if the ambient isn't roasting. Rough maths says that's maybe 120-160Wh over 8 hours, which sounds fine — 200Ah at 12V is nominally 2.4kWh and I'm not going below 20% SOC if I can help it, so usable is roughly 1.9kWh. Should be miles off.

But here's where my brain starts second-guessing itself:

• Is 45W peak draw going to cause any weird BMS behaviour on startup?
• Summer ambient in the motorhome could be brutal — does that tank the duty cycle badly enough to matter?
• I've got a Victron SmartShunt so I can actually log what's happening, but I'd rather not run a live experiment if someone's already done it

Also not currently hooked up to solar overnight (parked on a site with hookup but I'm trying to go off-grid for a weekend), so it's purely battery.

Suspect the answer is "yes it'll be fine, stop overthinking it" but I've been stung before by assuming nominally sensible numbers translate to real-world sensible outcomes.

@FormerCop done exactly this in my motorhome last summer — ran a Shoreline 35L chest freezer overnight off a single Fogstar Drift 200Ah.

The key thing nobody mentions is how efficiently a chest freezer runs versus an upright. Once it's pre-chilled, the compressor barely kicks in because cold air doesn't spill out every time you open it. Mine was pulling maybe 30-40Ah overnight in decent weather.

Where it gets dicey is ambient temperature — park somewhere sweltering and that compressor works overtime. Lost about 70Ah one brutal night in France.

The Drift's 80% DoD protection also means you're realistically working with 160Ah usable, so even worst-case you should be fine for one night. I'd pair it with a decent Victron BMV so you can actually watch what's happening rather than guessing.

@FormerCop a chest freezer overnight on 200Ah is basically fine — a typical small unit pulls maybe 30-50Ah over 8 hours once it's already cold, so you're using roughly 25% of your Fogstar's usable capacity, which means you've still got 75% left to feel smug about in the morning

@FormerCop I've run a small chest freezer off my 200Ah Victron setup many times — the key thing nobody mentions is ambient temperature matters loads. On a warm summer night the compressor cycles more frequently and you'll chew through noticeably more Ah than the textbook figures suggest.

Also worth checking your low voltage cutoff settings on the Fogstar BMS. Mine used to kick in at 20% SOC which is fine, but some people accidentally leave it too conservative and wonder why it trips early.

One other tip — pre-chill the freezer contents before switching to battery. Warm food = compressor working overtime all night.

You'll be fine on 200Ah though. Done this plenty. 🙂

@FormerCop worth adding to what @RetiredEngineer86 is getting at about ambient temp — the other thing that catches people out is how full (or empty) the freezer is. A nearly empty chest freezer has to work much harder because there's no thermal mass to hold the cold. Chuck a few bottles of frozen water in any spare space and it'll cycle far less frequently overnight.

Also worth checking your Fogstar Drift's low voltage cutoff settings if you haven't already — some come from the factory quite conservatively set, and you don't want it cutting out at 3am thinking it's flatter than it actually is.

Short answer though: yes, you'll be absolutely fine. 200Ah lithium and a small chest freezer overnight is very comfortable territory, assuming the freezer's pre-frozen and reasonably loaded.