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

Running my narrowboat through winter means I'm pretty paranoid about keeping a small chest freezer going when I'm moored without hookup. I've got a 200Ah lithium (Fogstar Drift, 12V) paired with a Victron SmartShunt so I can actually see what's happening with consumption.

My freezer is a Shoreline 60L chest unit — supposedly one of the more efficient ones — rated at about 45W but obviously it cycles rather than runs constantly.

Here's where I get a bit lost though:

• Overnight is roughly 8–10 hours for me
• I've read chest freezers typically run their compressor maybe 30–40% of the time in cool ambient conditions
• So rough maths: 45W × 40% duty cycle × 10hrs = ~18Ah consumed?

That sounds fine on a 200Ah battery, but I want to make sure I'm not missing something obvious. A few specific questions:

1. Is that duty cycle estimate realistic for a cold narrowboat (maybe 8°C ambient inside overnight)?
2. Should I be accounting for compressor startup surge causing any meaningful extra draw over time?
3. I'm keeping usable capacity to 80% DoD on the lithium — so effectively 160Ah available. Still seems like plenty, but is there anything else that'll be quietly nibbling at that bank overnight (Victron MPPT in standby, bilge pump controller, etc.)?

Has anyone done actual monitoring on something similar? Would love to see real SmartShunt data rather than back-of-envelope stuff if anyone has it.

@VictronPro mate, ran a 35L chest freezer off a Fogstar Drift 200Ah on my narrowboat last winter and it just scraped through — but "small" is doing a lot of heavy lifting in your question, because a poorly-insulated cheapo unit will drain you by 3am like a bad date.

Key things that saved me:

• Pre-chill the freezer before unhooking from shore power
• Stick a Victron BMV-712 on it so you're not guessing in the dark
• Keep the boat reasonably warm — freezers work harder when ambient temps swing

Realistically you're looking at 40-80Ah consumed overnight depending on the unit's duty cycle, so 200Ah gives you decent headroom if you're not also running everything else off the same bank.

@VictronPro worth checking whether your freezer has a decent compressor — the cheap ones cycle more aggressively in cold ambient temps which actually increases draw in winter, counterintuitively. My setup runs a 12V compressor fridge through a Victron SmartShunt and the logging data was eye-opening compared to what the spec sheet claimed.

Also bear in mind the Fogstar Drift's BMS will cut at around 10% SOC, so realistically you've got ~180Ah usable. If your solar input is minimal through the winter months that's your hard ceiling until you're moving again.

A small chest freezer should be fine, but I'd strongly recommend chucking a Victron BMV or similar on there first so you can actually see what it's pulling before committing to overnight unmonitored.

Done it in my van — a 200Ah Fogstar will handle a small chest freezer overnight no bother, but ambient temperature is your enemy in winter: colder air means the compressor barely kicks in, so you actually use less power than you'd think. The real killer is startup surge — make sure your Victron system can handle the inrush or you'll be waking up to a Victron alarm and warm fish fingers at 3am. 🐟

Done this on my tiny house setup — one thing nobody's mentioned yet is standby draw when the compressor's off. Some cheaper chest freezers have a controller board that pulls 8–15W constantly regardless. Worth sticking a plug-in energy monitor on it for 24hrs before you rely on it overnight.

Also, in winter the freezer works harder if it's sat somewhere that drops below about 10°C — counterintuitive but true, the compressor control gets confused and either over-runs or shuts off depending on the model.

@VictronPro if you've got a Victron BMV or SmartShunt, set a low SOC alarm at around 20% so you're not caught out. 200Ah should be fine but margins get tight in a cold snap.

Good points all round here. One thing worth adding — on a narrowboat you'll want to factor in your other overnight loads too. Lighting, bilge pump, any heating controls etc. all nibble away at that 200Ah more than people expect. Also, with the Fogstar Drift specifically, you're working with usable capacity down to around 80-90% DoD comfortably, so you've got plenty of headroom — but do the full calculation including everything running, not just the freezer in isolation. @JasonMoore makes a fair point about standby draw; worth sticking a simple energy monitor on the freezer for a night to get your actual figures before committing to a longer trip without hookup.