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

Running this exact scenario at my shepherd's hut and trying to get the numbers straight before I commit to anything.

Currently have a 200Ah Fogstar Drift LiFePO4 (so roughly 2.56kWh usable at 100% DoD, though I'd keep it above 20% in practice — call it ~2kWh realistically). Paired with 400W of solar but obviously that's irrelevant overnight.

The chest freezer in question is a small 60L unit, rated at ~90W but I know that's peak compressor draw, not average consumption. From what I can find online it's probably cycling on/off and averaging somewhere around 0.5–1kWh per 24 hours depending on ambient temp.

So the maths seems fine — overnight is maybe 10–12 hours, that's roughly 0.25–0.5kWh worst case? But I'm second-guessing myself because:

1. My setup is also running a few LED lights and phone charging overnight (~50W combined maybe?)
2. Ambient temps in the hut can drop quite low which I'd assume affects compressor runtime
3. I'm going through a Victron MultiPlus so there's inverter efficiency losses to factor in

Does anyone have real-world figures from a similar setup? Particularly whether 200Ah is actually comfortable for this, or whether I'd be scraping through to morning and stressing the battery before the panels kick back in.

FrankReid | 847 posts

@CurrentAffairs Good news is LiFePO4 is well suited to this. The key variable you're missing is which chest freezer - they vary enormously. A decent small chest freezer (say 60-100L) in a cool environment might average 30-50W, meaning roughly 300-500Wh overnight across 10 hours. Your 2.56kWh gives you plenty of headroom there.

However, compressor startup draw can spike significantly, so make sure your inverter can handle that surge.

Worth checking the EU energy label if your freezer has one - the annual kWh figure divided by 365 gives you a rough daily average to work from.

What's the ambient temperature in the shepherd's hut overnight? Warmer surroundings mean the freezer works harder. That single factor can double your consumption in summer.

IanHenderson79 | 234 posts

Running a small chest freezer off my static caravan setup so can chip in here. The freezer's ambient temperature matters massively — mine pulls way less in winter than summer. Also worth knowing the compressor duty cycle rather than just the watt rating on the label.

Rough numbers from my experience: a decent 60-70L chest freezer might average 30-40W once settled, so overnight (say 10hrs) that's maybe 300-400Wh. Your 2.56kWh Fogstar gives you plenty of headroom on paper.

Main thing I'd add that @FrankReid hasn't touched on — start-up surge. Chest freezer compressors can spike 3-4x rated watts on kick-in. Make sure your inverter handles that without tripping. I got caught out with a cheap unit before switching to Victron.

MarinePhil | 1,203 posts

Done this exact calculation for my van conversion and later my motorhome backup setup, so here's the bit others haven't covered:

Startup surge is your hidden enemy. Small chest freezers can pull 3-5x their rated wattage on compressor kick-in — usually 300-500W surge for half a second. Your Fogstar Drift handles this brilliantly (LiFePO4 laughs at surge loads), but make sure your inverter is rated for it.

A rough real-world figure: a decent chest freezer in a well-insulated shepherd's hut will cycle maybe 30-40% duty cycle overnight, so you're realistically looking at 400-600Wh consumed over 8 hours. Your 2.56kWh gives you comfortable headroom.

Where people come unstuck is ambient temperature — a freezer works harder in summer. Factor that in before assuming winter figures apply year-round.

WezFrost | 412 posts

Worth flagging something nobody's mentioned yet — ambient temperature at the shepherd's hut matters massively here. My narrowboat chest freezer draws nearly double in summer compared to winter because it's working harder against warm air.

Also check the compressor startup surge. My little 30L unit pulls about 4-5x its rated wattage for half a second on startup — not a huge deal for a decent inverter but worth knowing your Fogstar BMS can handle the spike without tripping.

200Ah should be fine overnight if the freezer's well-stocked (thermal mass helps loads) and you're not in a heatwave. But I'd want at least a basic solar top-up during the day rather than running the battery dry every 24hrs — that'll age it faster than you'd like.