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

Running my boat through the summer months, so this feels quite relevant to me personally — though I've not tried it myself yet and wanted to get some opinions before committing.

I've got a 200Ah lithium (Fogstar Drift, for reference) connected to a Victron SmartSolar MPPT with around 400W of panels on the roof. During the day, charging is generally fine. It's the overnight draw I'm trying to get my head around.

The chest freezer in question is one of those 50-litre tabletop units — a Subcold, if anyone's familiar. Rated at around 90W but obviously it's not running continuously. From what I've read, a well-insulated chest freezer might only run its compressor 30–40% of the time once it's up to temperature.

So roughly speaking:

• 90W × ~35% duty cycle = ~31.5W average draw
• Over 10 hours overnight = ~315Wh
• That's roughly 26Ah at 12V

On paper, that looks very manageable. But I'm wary of real-world variables — ambient temperature on the boat in summer, how full the freezer is, whether my mental arithmetic is actually correct...

Has anyone run something similar long-term? Particularly curious whether the compressor cycling causes any headaches for the Victron, or whether the battery handles those startup spikes without complaint. I'd rather hear from people who've actually done it before I start stuffing frozen peas in there and hoping for the best.

@CallumHobbs depends massively on the freezer tbh. A decent efficient one (Dometic, Engel, etc.) might only pull 30-50Ah overnight in warm weather — well within your 200Ah. A cheap chest freezer though? Could be double that easily.

One thing worth noting on a boat — ambient temp around the compressor matters loads. If it's stuffed in a hot engine bay you'll kill your efficiency.

I'd chuck a basic energy monitor on it for a night or two before committing. Know your actual draw before sizing anything.

Also — what's your solar input for recharging during the day? 200Ah gets eaten fast if you're not topping it back up. Running a freezer 24/7 without decent solar behind it is a different conversation entirely.

@CallumHobbs worth thinking about usable capacity too — most lithium is rated to 80% DoD comfortably, so your 200Ah is really ~160Ah in practice if you want to protect cycle life.

I ran a similar setup last summer with a Fogstar 200Ah and a small Liebherr chest freezer. The freezer was pulling roughly 40Ah overnight, but ambient temps made a real difference — warmer nights meant the compressor cycled more frequently and consumption crept up noticeably.

The bit people miss is solar recovery time the following morning. If you're moored somewhere shaded or overcast, that 40-50Ah deficit can compound across consecutive nights pretty quickly.

On a boat I'd be looking at whether your alternator or any shore power can backstop you on cloudy days, rather than relying purely on the battery reserve holding up solo.

@Drift_Geek already touched on usable capacity but worth adding — ambient temperature is the killer variable nobody mentions. A chest freezer in a hot engine room or poorly ventilated cabin will cycle far more aggressively than one sitting in a cool space.

Also worth checking the startup surge current. Some cheaper compressor freezers pull 3-4x their rated draw on startup, which matters if your BMS has a conservative peak current limit.

@CallumHobbs — what battery are you actually running? If it's a Fogstar Drift or similar with a decent BMS you'll probably be fine, but a cheap no-name cell with an aggressive low-voltage cutoff can shut down well before you've used your theoretical 80%.

Run the freezer for 24hrs on shore power with a clamp meter first — takes the guesswork out entirely.

@CallumHobbs done exactly this on my narrowboat last summer — a halfway-decent chest freezer on a Victron/Fogstar setup will see you through the night no bother, provided you're not opening the lid every five minutes like my mate Dave who somehow can't resist checking if his lager is cold every single hour.