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

Running a small chest freezer off a 200Ah Fogstar Drift in my shepherds hut — anyone actually done the maths on this or do I need to just plug it in and pray?

The freezer I'm looking at is one of those 45L chest jobs pulling roughly 35–45W when the compressor kicks in, duty cycle apparently around 30–40% according to the spec sheet, so I'm guesstimating maybe 150–200Wh overnight (let's call it 10 hours). On paper that sounds perfectly manageable off a 200Ah/2.56kWh bank, but I've been burned before by "on paper" calculations when real-world parasitic loads, ambient temperature, and the freezer deciding to run flat-out all night because it's July in the UK (both of those things happening simultaneously being admittedly rare).

Few specifics that might matter:

• Battery: 200Ah 12V lithium (Fogstar Drift), so roughly usable capacity around 2.4kWh keeping above 20% SoC
• Inverter: Victron Phoenix 12/375 — should be fine for the startup surge but worth flagging
• Solar charging: Small 200W panel array, so daytime replenishment is limited
• No grid hookup — this is genuinely off-grid in a field in Shropshire

Main concern is whether the compressor startup surge causes any grief with the Phoenix, and whether overnight I'm eating through significantly more than my estimates suggest. Anyone running something similar in a static off-grid setup rather than a motorhome? Most threads I find are van-life people with far beefier setups.

@CharlieCampbell66 done exactly this on my static caravan — a 50L chest freezer pulls about 100-150Wh overnight once it's already cold, so your 200Ah Fogstar (roughly 2kWh usable) will laugh at it, assuming you're not opening it every five minutes like my husband does.

@CharlieCampbell66 the maths works out reasonably well actually. A 200Ah Fogstar at 12V gives you ~2400Wh theoretical, but you're realistically working with around 1800-1900Wh usable (don't hammer lithium below 10-20% if you want the cells to last). Chest freezers are surprisingly efficient — the compressor cycles maybe 30-40% of the time once it's at temperature. Where it gets spicy is the initial pulldown if you're starting warm; that's when you'll see proper current spikes. Chuck a clamp meter on it for the first couple of hours rather than guessing.

The bigger question is what's recharging the Fogstar during the day — solar array size? Because overnight is one thing, but a cloudy Scottish October week is a different conversation entirely. 😄

Worth adding from narrowboat experience — ambient temperature makes a massive difference to your real-world consumption. My freezer uses noticeably more power in summer when the boat interior gets warm. If your shepherd's hut isn't well insulated or sits in direct sun, factor that in.

Also worth checking whether your freezer has a decent compressor (Secop/Danfoss-based units are far more efficient than cheap Chinese compressors). The difference between a quality 50L unit and a budget one can be 30-40% in actual draw.

@TracyAllen is right about the usable capacity — and on lithium you'll want to stay above 20% SOC ideally, so more like 1600-1800Wh practically available on that Fogstar.

What's your solar situation? Without daytime recharging you're essentially doing one cycle per day which adds up over a season.

@CharlieCampbell66 done exactly this but in my static caravan — one thing nobody's mentioned yet: don't forget the freezer's startup surge can be 3-5x the running wattage, so make sure your inverter isn't undersized or you'll get that lovely 3am alarm going off 🔔 — my Victron MultiPlus handles it fine but I learned that lesson the hard way with a cheaper unit.