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

Got a Fogstar Drift 200Ah sitting in the motorhome and I'm trying to work out if it'll comfortably run a small chest freezer overnight without hammering the battery too hard.

The freezer I'm looking at is one of those 12V compressor units — roughly 40-45 litre capacity. Specs say it draws around 45W at peak but obviously the compressor cycles on and off, so real-world draw will be lower.

My rough maths:

• Usable capacity on a 200Ah LiFePO4 = ~190Ah (95% DoD)
• At 12V that's roughly 2.28kWh
• A small chest freezer might average 15-25W over 24hrs depending on ambient temp

So on paper it looks fine, but I'm not accounting for:

1. Ambient temps (parked in full sun can get brutal even overnight)
2. How often the lid gets opened during the day
3. Whether I've got anything else pulling from the same battery

Anyone actually running a setup like this? I've got a 100W solar panel on the roof which obviously does nothing overnight, so it'd be purely battery until morning.

Is 200Ah realistic for this, or should I be looking at adding a second battery before I commit to buying the freezer? Would rather ask before spending the money and finding out it's marginal.

@SuffolkSolar done exactly this in my van conversion last summer. The key thing people miss is duty cycle — a chest freezer doesn't run continuously, it cycles on and off. Mine averaged around 30-40Ah overnight once the contents were already frozen down.

200Ah Fogstar Drift gives you roughly 160Ah usable at 80% DoD, so you've got plenty of headroom. Main questions I'd ask:

• What's the ambient temperature where you're parked?
• Are the contents already frozen or starting warm?
• What inverter are you running it through — efficiency losses matter

Warm contents or a hot night will absolutely hammer your consumption. I'd stick a battery monitor on it first night and just watch what it's actually pulling rather than guessing. The Victron BMV-712 is what I use — worth every penny for exactly this kind of thing.

@SuffolkSolar my Fogstar Drift 200Ah runs a Whynter 35L chest freezer through summer nights no bother — but winter's where it gets spicy, compressor barely kicks in and you're laughing, meanwhile a hot August bank holiday and you're watching your State of Charge drop like my motivation on a Monday morning.

Key number to find: your freezer's actual watt-hours per 24hrs (usually on the manufacturer site, not the nameplate wattage which is meaningless). Divide by 2 if you're sensible about not going below 50% SoC on lithium.

Rule of thumb though — small chest freezer typically pulls 20-45Wh per hour depending on ambient temp, so overnight (say 10hrs) you're looking at 200-450Wh worst case. Your 200Ah at 12V is 2,400Wh usable. You'll be fine, mate.

@GoldenMechanic is right about duty cycle being the real number to chase, but also worth factoring in ambient temp — freezer works harder in a hot motorhome than sitting in a cool garage.

I run a 12v compressor fridge (not quite the same I know) off a 200Ah Fogstar in my static and the draw varies massively depending on season.

Rough maths: if the freezer pulls ~40W average duty-cycled, that's maybe 3-4A. Over 10hrs that's 30-40Ah. Well within a 200Ah lithium's usable capacity.

You'd want to check the actual wattage on the freezer label though — some of those budget chest freezers are surprisingly inefficient. Worth chucking a Victron energy meter or even a cheap Bluetooth shunt on it first to see real-world draw before committing overnight.

@SuffolkSolar one thing nobody's mentioned yet — starting surge current. Chest freezer compressors can pull 3-5x their running draw on startup, so check your Fogstar's continuous and peak discharge rating against your freezer's LRA (Locked Rotor Amps). The Drift handles this well in my experience, but it's worth confirming.

Also: battery state of charge matters enormously. Going into the night at 80% vs 100% is effectively losing 40Ah before you've even started. With a 200Ah LiFePO4 you realistically want to stay above 20% SOC, so your usable overnight window is roughly 160Ah — usually plenty, but run the numbers with your specific freezer's rated wattage × duty cycle first.

What freezer model are you actually running? That'll make this calculation much more concrete.

Good point from @DailySolar on the surge — worth checking your Fogstar's BMS can handle it, though the Drift series is pretty robust in that regard.

The number I'd actually focus on is usable capacity. Your 200Ah at 12V is roughly 2.4kWh, but you'll want to stay above 20% to keep the battery happy long-term, so call it ~1.9kWh realistically available.

A typical small chest freezer might average 30-60W once you account for duty cycle — so overnight (say 10 hours) you're looking at 300-600Wh consumed. That's well within your budget even accounting for inverter losses.

Where it gets trickier is shoulder seasons — freezer runs harder, nights are longer, and you may not have solar replenishment. I'd run a monitoring week before relying on it fully.