Anyone know if a 200Ah lithium battery is enough to run a small chest freezer overnight?

Running a small chest freezer in my van conversion and trying to work out if my 200Ah Fogstar Drift is going to cut it overnight without solar input.

The freezer is a Alpicool C15 (15L) — pulls about 45W when the compressor kicks in but obviously it cycles, so real-world draw is probably more like 15-20Ah per 24hrs from what I've read? Though that's in a temperate environment and I'm planning a trip up to Scotland in October so ambient temps will be lower which should help efficiency I think.

My concerns:

• I've also got a Victron SmartShunt so I can monitor it properly, but haven't done a real overnight test yet
• Van will be parked up with no solar input from roughly 6pm to 9am
• I've got a 200W Renogy panel but it's basically useless once the sun goes down obviously 😅

So the question is — is 200Ah (usable \~180Ah with the 90% DoD I try to stick to) realistically enough headroom when you factor in other loads like lighting, phone charging, a small fan heater on low occasionally?

Gut feeling says it'll be fine but I don't want to get stranded in the Highlands with a dead bank and defrosted food. Has anyone run a similar setup and got actual figures from their SmartShunt or a battery monitor? Wondering if I should look at adding a second 100Ah battery before the trip or if that's overkill.

@Brummie86 short answer: probably, but it depends on ambient temp and how full the freezer is.

Those little compressor units are surprisingly efficient — the Alpicool draws maybe 35-45W when running but it's not running constantly. Duty cycle is the key figure. In a warm van it'll work harder, cold night it'll barely kick in.

Rough maths: assume 20-25Wh average per hour overnight (8hrs = ~200Wh). Your 200Ah Fogstar at 12V is 2400Wh nominal. Even keeping above 20% SOC you've got well over 1500Wh usable. You're fine.

Main caveat — don't let the van interior bake all day before you go to sleep. A warm box pulling the temp down hammers your battery far more than steady-state overnight running ever will.

Good question to stress-test before you're somewhere remote with melting food.

What @ExChippie hasn't mentioned is duty cycle — that little Alpicool won't be running its compressor constantly. In my experience with similar 12V compressor units, you're looking at maybe 30-40% duty cycle in mild overnight temps, so your actual draw is far less than the peak wattage suggests.

Your Fogstar Drift is a proper bit of kit — assuming you're not draining below 20%, you've realistically got around 160Ah usable. A C15 pulling ~4Ah average overnight is nothing against that.

The killer scenario is a heatwave with the freezer half-empty. Pre-freeze the contents before you go off-grid — thermal mass is your friend. Packed tight, those compressors barely break sweat.

You'll be fine.

A 200Ah Fogstar Drift sitting at 80% DoD gives you 160Ah usable — those Alpicool units typically sip around 30-45Ah overnight once they've hit temp, so you're almost certainly fine unless you're parked in the Sahara or, y'know, Birmingham in August.

Good shout from @MarineClare on the numbers. One thing worth adding — starting temperature matters massively. If your freezer's already at temp when the sun goes down, duty cycle drops significantly. Pre-cooling while you've still got solar coming in is the move.

Had similar on my narrowboat with a slightly bigger unit — a well-insulated freezer that's already cold barely touches the battery overnight. Throw some frozen water bottles in to fill dead space if it's not full, thermal mass is your friend.

Also worth chucking a battery monitor on if you haven't already — Victron BMV-712 will show you actual Ah consumed so you're not guessing. One night of data tells you more than any calculator.

@MarineClare's maths checks out, but nobody's mentioned that "overnight" in a Scottish January is roughly 14 hours of pitch black and -5°C ambient — which actually helps the freezer efficiency weirdly enough, until your Fogstar starts throttling in the cold itself. 🙃

Run it on my narrowboat through winter and the Victron BMV-712 data doesn't lie — duty cycle drops dramatically once ambient temps plummet, so your 30-45Ah estimate could be generous rather than pessimistic depending where @Brummie86 is parked up.

Short answer: probably fine, but I wouldn't bet a chest of frozen venison on it without a shunt and a night's worth of logged data first.