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

Running a small chest freezer on my narrowboat overnight and wondering if my single 200Ah (Fogstar Drift 12V) is going to cope, or if I'm about to wake up to a puddle of defrosted disappointment.

The freezer is a Subcold Ultra 60 — pulls about 60W when the compressor kicks in, but obviously it's not running constantly. From what I can tell it cycles maybe 30-40% of the time once it's up to temperature, so rough maths says something like:

• 60W × ~35% duty cycle = ~21W average draw
• Over 8 hours = ~168Wh
• At 12V that's roughly 14Ah

Which sounds fine — 200Ah lithium at 80% DoD gives me 160Ah usable, so 14Ah should be nowt. But I'm skeptical of my own optimistic maths, because I've been wrong before (RIP my old AGM bank, 2019–2021, gone too soon).

Questions I'm actually not sure about:

1. Does a chest freezer's compressor have a nasty startup surge that causes any real-world issues with a Victron MultiPlus 12/1200?
2. Is a 35% duty cycle realistic for a chest freezer in a UK autumn, or am I being naive?
3. Anyone actually done this and got data from a Victron Cerbo or similar to share?

The boat's solar will be basically useless overnight obviously, so it's purely battery capacity I'm relying on. Generator top-up in the morning is an option but I'd rather not run it daily if the numbers genuinely work.

@OffGridGeek a chest freezer typically pulls around 30-50Wh average overnight (they cycle, not run continuously), so your 200Ah Fogstar is sitting on roughly 2.4kWh — you'd need to be spectacularly unlucky to lose the battle against a bag of frozen peas.

Just don't also try charging an EV off it at 3am like some people have attempted. 🙃

@OffGridGeek welcome to the forum, great first post with a very practical question!

@KangooBuild has the consumption side covered, so I'll add the other half of the equation: your Fogstar Drift is a solid choice — 200Ah at 12V gives you 2,400Wh theoretical capacity, and assuming you're observing the sensible 80% DoD limit, that's ~1,920Wh usable.

Even a moderately inefficient small chest freezer averaging 40-50Wh overnight would only draw perhaps 300-400Wh across 8 hours. You've got plenty of headroom.

The thing to watch on a narrowboat specifically is your inverter efficiency if you're running AC — a cheap inverter can bleed 10-15W just sitting idle. A DC-native freezer (like the Brass Monkey range) sidesteps that entirely.

What's your charging setup? Solar, alternator, shore power? That determines whether you'll be topped back up by morning.

Mine ran a chest freezer for 18 months on a single Fogstar 200Ah — only discovered it was struggling when I added a second battery and realised how smugly comfortable the first one had been all along.

@OffGridGeek on a narrowboat the real wildcard is ambient temp — engine room or well-ventilated locker? A freezer works harder in a warm space, so placement matters more than people realise.

Also worth checking the actual watt-hour draw with a simple energy monitor (Victron BMV or even a cheap inline meter). The 30-50Wh average @KangooBuild mentioned is realistic for a well-insulated chest freezer in a cool spot, but I've seen poorly placed units pull double that.

One practical tip: pre-cool the freezer well before you disconnect from shore power or stop the engine. Thermal mass is your friend — a full freezer holds temp far better than a half-empty one.

Your Fogstar Drift should cope fine in most scenarios, but monitor it for a few nights before trusting it fully.