Anyone know if a 200Ah lithium battery is enough to run a small chest freezer overnight?

Running a small chest freezer in my static caravan off a 200Ah LiFePO4 (Fogstar Drift) and genuinely not sure if I've got enough capacity to get through the night without killing the battery.

The freezer is a Klarstein 50L chest freezer, rated at about 80W but obviously it duty cycles — doesn't run constantly. From what I can work out it's probably pulling maybe 30-40Wh per hour on average? So over say 10 hours overnight that's potentially 300-400Wh.

On a 200Ah at 12V that's 2400Wh total, but I only want to draw down to 50% SOC to keep the battery healthy long-term. So realistically I've got around 1200Wh usable.

On paper that looks fine but a few things are nagging at me:

• Ambient temp in the caravan overnight — does a colder environment make the freezer more or less efficient?
• The compressor startup surge — does that cause any issues with the Victron inverter or is it a non-issue on modern lithium setups?
• I've got a 100W solar panel but obviously that's doing nothing overnight, so I'm entirely on stored capacity until morning

Has anyone actually done this with a similar setup? I've read conflicting things about chest freezers being surprisingly efficient vs. them being a silent battery killer if the insulation isn't great or you open them too often.

Also — does the freezer need to be running for a while before relying on it to actually keep things frozen, or will it maintain temp fine through the night even if the battery voltage dips a bit?

@SmartSolarNerd been exactly in your shoes — had a small chest freezer humming away in my van conversion and the anxiety of checking voltage at 6am is real.

Short answer: you're probably fine, but it depends on the freezer's duty cycle. Most small chest freezers pull 60–100W but only run the compressor maybe 30–40% of the time, so you're looking at roughly 150–250Wh overnight (8 hours). Your Fogstar Drift at 200Ah gives you around 2,048Wh usable — that's plenty of headroom.

The sneaky culprit is ambient temperature. Stick that freezer somewhere warm and the compressor runs overtime, chewing through your bank faster than you'd expect.

Chuck a Victron BMV on there if you haven't already — knowing your actual consumption rather than guessing is genuinely life-changing. Worth every penny.

Depends massively on the freezer tbh. Small chest freezers typically draw 30-60W but they're not running constantly — duty cycle is maybe 30-40% so you're looking at roughly 15-25W average.

Over 8hrs that's ~120-200Wh. On a 200Ah (2560Wh usable at 80%) you've got loads of headroom on paper.

Real-world though — ambient temp matters a lot. Summer van = freezer works harder = duty cycle shoots up. Running mine through last July was noticeably heavier on the Fogstar than winter.

Stick a Victron energy meter or even a cheap plug-in watt meter on it for a night before you commit. Know your actual numbers rather than guessing.

What @Brummie86 is getting at is the key bit — duty cycle is everything here.

Real talk though: 200Ah Fogstar at 80% usable = 160Ah practical. Overnight is roughly 10-12hrs. If your freezer's pulling say 45W average including off cycles, you're looking at maybe 450-540Wh. At 12V that's 37-45Ah. Should be fine on paper.

But — ambient temp in a static caravan matters loads. Hot summer night? That compressor's working harder, duty cycle shoots up.

I'd just chuck a basic energy monitor on it for a few nights and get actual numbers rather than guessing. Owl or similar, dead cheap.

Also check your BMS low voltage cutoff. Some cheaper units get twitchy around 20% SOC and that's when freezers hate you.

What @ZFS_OffGrid and @Brummie86 have covered on duty cycle is spot on. One thing worth adding — ambient temperature matters loads here. A chest freezer in a warm static caravan works harder than one sitting in a cool outhouse. Summer nights could push that duty cycle up noticeably.

For backup peace of mind I'd stick a cheap inline energy monitor on it for a few days and get actual numbers from your freezer in your conditions. I've got a Victron BMV-712 on my setup and that kind of real data is worth more than any estimate.

200Ah is probably fine but I wouldn't assume it — measure first.

Good coverage from @Brummie86, @ZFS_OffGrid and @TelScott75 already on duty cycle and ambient.

One angle nobody's touched on: inverter efficiency losses. If you're running that freezer via an inverter rather than a native 12V compressor unit, factor in roughly 10-15% additional draw on top of the freezer's rated consumption. A cheap inverter sitting at light load can be surprisingly thirsty just idling.

Also worth knowing — the Fogstar Drift's BMS will hard-cut at low voltage. You won't get a gentle warning, the freezer just dies. I'd strongly recommend setting a low voltage disconnect (Victron BMV relay output works well for this) at around 20% SOC so you get a controlled shutdown rather than a BMS trip mid-night.

200Ah should be workable, but instrument it properly before you trust it. A Victron SmartShunt costs around £60 and removes all the guesswork.

Right, @RetiredSquaddie's teased us all with a mystery angle — don't leave us hanging, mate!

What I will add, having run a small chest freezer through a shepherd's hut build for the better part of two winters: the startup surge is the sneaky villain nobody mentions until their BMS trips at 2am.

My little Beko chest freezer pulls roughly 5-6x its running wattage on compressor kick-in. The Fogstar Drift handles it fine — Fogstar's discharge rate is decent — but if your inverter is undersized or your BMS has a conservative peak current threshold, you'll get nuisance shutdowns rather than a flat battery.

Worth checking:

• Your inverter's surge rating
• BMS peak discharge amps
• Whether the freezer has a "soft start" (most don't)

The 200Ah is almost certainly enough. Whether your system will allow it is the real question.