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

Running a small chest freezer overnight is something I've been trying to nail down the maths on for my motorhome setup, so hoping someone with real-world experience can chime in.

I've got a Fogstar Drift 200Ah LiFePO4 and I'm looking at adding a chest freezer — probably something in the 30–40 litre range like a budget unit from Argos or a dedicated compressor unit like the Brass Monkey or similar.

The bit I'm struggling with is the variability. Duty cycle seems to be the critical factor — I've seen people quote anything from 20–50% duty cycle depending on ambient temperature and how full the freezer is. At say 30–35W running draw, that's potentially 7–8Ah per hour at 12V, which over 8 hours of overnight use puts you somewhere around 56–64Ah assuming a reasonably efficient duty cycle. That sounds like the 200Ah bank should cope comfortably, especially since LiFePO4 gives you usable capacity down to around 80–90% DoD without stressing the cells.

But my concerns are:

• Ambient temps — I'm often parked with no shade and summer ambient can push the compressor to run almost continuously
• Starting current spikes — does this cause any BMS issues on the Fogstar?
• Solar replenishment — I've got 400W of panels so daytime recovery should be fine, but purely overnight I want to know I've got enough headroom

Has anyone actually monitored this with a Victron BMV or similar rather than just estimating? Real consumption figures would be genuinely useful rather than spec sheet numbers.

@LuckyHiker yes, very doable in most cases but the devil's in the detail.

Chest freezers are brilliant for off-grid because the duty cycle is surprisingly low — typically 20-40% once they're at temperature. A small one (say 60-80L) might pull 35-45W when running, so average consumption over 8 hours could realistically be 150-250Wh depending on ambient temperature and how often it's opened.

Your 200Ah Fogstar at 12V gives you ~2400Wh theoretical, but you'll want to stay above 20% SoC, so working capacity is roughly 1920Wh — still plenty of headroom.

Key variables:

• Ambient temp (hotter = compressor runs longer)
• Pre-cooling the freezer before relying on battery
• Whether you've got any solar topping it up overnight

On my narrowboat setup the chest freezer barely dents the bank overnight. What's the wattage listed on the freezer's label?

Ran this exact scenario before settling on my static caravan setup. The compressor duty cycle is the variable people underestimate — in summer ambient temps a small chest freezer can pull 40-60W average once you factor in the cycling, not just the running wattage. Over 8 hours that's potentially 320-480Wh.

On a 200Ah battery (assuming Fogstar Drift or similar at 12V, so ~2400Wh usable at 100% DoD, though I'd cap at 80%), you're looking at comfortable headroom if the freezer is pre-frozen and well-insulated.

Where it falls apart: warm ambient temps, poorly stocked freezer, lid opened repeatedly, or a cheap compressor with terrible efficiency. Worth checking your specific model's actual power draw with a plug-in energy monitor before committing — manufacturer specs are often optimistic.

@LuckyHiker done this on my narrowboat for two winters — the freezer's actually easier than people think, it's the moment you open it at 2am for a midnight Cornetto that kills your runtime.

@LuckyHiker done this in my van conversion with a similar setup. The bit nobody mentions — ambient temperature matters massively. Parked in Scotland in October vs a French campsite in August, same freezer, completely different consumption.

A rough rule of thumb I use: small chest freezer averages maybe 30–45Wh/hr in mild conditions. So overnight (say 10 hours) you're looking at 300–450Wh. On a 200Ah lithium at 12V that's 2.4kWh usable — loads of headroom really.

What's your inverter situation though? If the freezer's 240V you're losing a bit through conversion. DC compressor fridges/freezers are way more efficient for off-grid. Worth checking if the Fogstar unit has a direct DC option.

Also factor in what else you're running overnight — lights, a CPAP, phone charging — it all nibbles away.

Great thread! @WonkyMender is spot on about ambient temps — I'd add that state of charge matters hugely too. Don't run a 200Ah Fogstar Drift below 20% if you can help it; you're effectively working with 160Ah usable.

Real-world from my setup: a 60L chest freezer pulls roughly 25-35Wh per hour once it's established its thermal mass. Over 10 hours that's 250-350Wh — well within a 200Ah (2560Wh) bank even accounting for inverter losses.

Key tips:

• Pre-freeze the contents before switching to battery
• A full freezer holds temp far better than a half-empty one
• Check your inverter efficiency — cheaper units waste 10-15%

You should be absolutely fine with a single 200Ah battery for overnight, though I'd always sleep easier with a bit of solar topping things up at dawn.