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

Running a small chest freezer off a 200Ah lithium (Fogstar Drift 12V if it matters) and trying to work out if I've got enough capacity to get through the night without the solar doing anything useful.

The freezer is a SilverCrest 60L — pulled about 90W when I measured it running, but obviously it's cycling on and off rather than running continuously. From what I've read the compressor duty cycle on a well-insulated chest freezer can be fairly low, maybe 30-40%?

So rough maths:

• 90W × say 35% duty cycle = ~31W average draw
• 8 hours overnight = ~250Wh
• 200Ah × 12V = 2400Wh usable (at 80% DoD = 1920Wh)

On paper that looks very comfortable, but I'm second-guessing myself because:

1. Ambient temperature — the freezer is in an uninsulated outbuilding and it's been cold lately. Does that actually reduce compressor run time or does it somehow increase draw?
2. Startup surge — does the inverter need to be significantly oversized to handle the compressor kicking in, or is that less of an issue with modern chest freezers?
3. My maths is wrong somehow — wouldn't be the first time

Currently running a Victron MultiPlus 12/1200 as the inverter so that side should be fine. Just want a sanity check before I commit to leaving it running overnight unattended. Has anyone done something similar and can confirm real-world figures?

Hey @Taffy62, should be fine in most cases. Chest freezers are quite efficient compared to uprights — a small one (under 100L) typically draws around 30-60W when the compressor's running, but it cycles on and off, so average consumption overnight (say 8 hours) is often only 150-250Wh in a cool ambient environment.

Your Fogstar Drift is 200Ah × 12V = 2.4kWh usable (roughly 2kWh being cautious), so you've got plenty of headroom even if it's a warmer night and the compressor runs more frequently.

Worth checking the actual watt-hour figure on your freezer's label though — ambient temperature makes a big difference. If it's sitting in a hot garage in summer, consumption can roughly double. A cheap plug-in energy monitor like a Brennenstuhl will give you real figures within a day or two.

Depends heavily on ambient temp and how full it is. A full freezer holds cold much better than an empty one — if yours is half empty, chuck some bottles of water in.

Rough numbers from my own setup: small chest freezer (~100L) draws maybe 30-40Ah per 24hrs in a cool shed. So overnight (say 10 hours with no solar) you're looking at 15-20Ah. Your 200Ah Fogstar has loads of headroom even accounting for the recommended 80% DoD.

Worth checking your actual draw with a clamp meter or a decent battery monitor — Victron BMV-712 will show you exactly what's happening overnight. Don't just guess.

Summer kitchens and hot garages change the maths considerably though. If it's sitting somewhere warm, could easily double that consumption.

Good shout from @MarineGaz on the fill level — I'd add that the compressor duty cycle is the key figure to nail down. Most small chest freezers run maybe 20-30% of the time once stable, so actual draw overnight (say 10 hours) is often only 3-5Ah per hour effective rather than the rated wattage.

Your Fogstar Drift at 200Ah gives you roughly 160-170Ah usable before you're pushing it — more than enough headroom there.

Worth sticking a plug-in energy monitor on it for a few days first though. Real-world figures always surprise you. Mine pulled far less than the spec sheet suggested once it had stabilised at temperature.

One thing to watch: if the freezer's been running off mains and you're switching over, that initial pull-down cycle will be heavier than normal overnight running.

The Fogstar Drift is 200Ah but you're not getting the full 200Ah usable — Fogstar quote 80% DoD as the sweet spot, so realistically you're working with ~160Ah before you're stressing the cells.

Worth double-checking: is your freezer 12V direct or running via an inverter? If it's AC through an inverter you're losing 10-15% to conversion losses before the compressor even sees a watt. That eats into your overnight budget faster than most people expect.

Also check the starting surge on the compressor — most small chest freezers pull 3-4x running current on startup. Your Fogstar will handle it fine, but if you've got a small inverter it might not.

What's the actual wattage on the freezer nameplate? Running blind without that figure makes this whole discussion a bit speculative.