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

Got a Fogstar 200Ah 12V lithium sat in the van doing a reasonable impression of an expensive paperweight, and I'm wondering if it'll cope with running a small chest freezer through the night without me waking up to warm prawns and regret.

Setup context if it helps: I've got a 400W solar array on the roof (two Renogy 200W panels in parallel) feeding into a Victron SmartSolar MPPT, so the battery should be reasonably topped up by dusk — assuming British weather doesn't decide to spend the whole day being aggressively grey.

The freezer in question is a 30-litre chest unit, rated at about 45W running load, but obviously that's a compressor so it's cycling rather than drawing constantly. I've seen figures thrown around suggesting maybe 30-50% duty cycle overnight, which would put me somewhere in the region of 35-50Ah consumed across, say, 10 hours — that sounds fine on paper but I've been wrong before (see: the great inverter incident of 2023).

My main questions are:

• Is my duty cycle maths roughly right, or am I being optimistic?
• Does ambient temperature in the van massively affect how hard the compressor works? (We're talking summer UK, so... 14°C at night if I'm lucky)
• Any brands people would actually recommend for a van-sized chest freezer that plays nicely with 12V systems?

Basically I want cold beers and functioning fish without buying a second battery, but I'll buy the second battery if everyone tells me I'm being an idiot.

@Lefty72 Short answer: probably yes, but the devil's in the details.

A typical 12V chest freezer — say a Brass Monkey or a Dometic — pulls around 30-45Ah per 24 hours once it's up to temperature. So overnight (8-10 hours) you're realistically looking at 15-25Ah drawn down.

Your Fogstar 200Ah gives you roughly 160Ah usable before you're stressing it. You've got bags of headroom if the freezer is pre-chilled and not fighting a 30°C van interior.

Where people come unstuck:

• Ambient temperature — compressors work harder in the heat
• Starting current spike — make sure your wiring and fuse are rated properly
• Solar input during daylight hours massively changes the equation

What's your charging situation? No solar topped up during the day and that battery will eventually lose the battle over several consecutive nights.

Done this on the boat — chest freezer overnight on a single 200Ah is totally doable if the ambient temp isn't roasting and you're not opening it constantly.

Worth knowing though: compressor starts are the killer. Mine would spike to ~8-9A on startup then drop to 2-3A running. Victron BMV caught it all beautifully once I wired it up properly.

One gotcha nobody mentions — pre-chill everything before you go to sleep. Warm food = compressor runs flat out all night = dead battery by 4am, voice of experience there 😬

What freezer model is it? Some of the cheaper ones are terrible on efficiency compared to something like a Brass Monkey or Iceco.

Don't forget the Fogstar's got a BMS that'll throw a strop if you somehow manage to actually drain it — so your "paperweight" has its own self-preservation instincts, much like me at a motorhome rally buffet.

Worth adding a bit of precision to what @LiFePO4Nerd is hinting at: usable capacity on that Fogstar 200Ah is realistically around 180–190Ah (Fogstar's BMS is fairly conservative at the low end, which is sensible). A small chest freezer typically draws somewhere between 3–5A average at 12V once it's at temperature — so you're looking at roughly 36–60Ah over a 12-hour night. That's well within budget even accounting for inverter losses if you're running an AC unit.

Key variable nobody's mentioned yet: how cold the freezer already is when you start. Pre-chill it thoroughly before sunset so the compressor isn't working overtime from warm. Also, lid seal integrity matters enormously — a degraded seal absolutely murders efficiency. Worth running a damp tissue around the seal edge to check for draw.

Ambient temperature as @BayLisa says is the other major factor — a warm shed is a different proposition to an unheated outbuilding in January.