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

Running a Fogstar Drift 200Ah in my motorhome and genuinely cannot decide if I'm being optimistic or delusional about keeping my little 40L chest freezer alive overnight without the solar doing anything useful after dark 🌙

Setup is pretty straightforward — 200W of Renogy panels feeding into a Victron SmartSolar, and the freezer is one of those supposedly "efficient" compressor types that claims 0.4kWh per 24 hours, though I suspect that figure was measured in a Norwegian laboratory at -2°C ambient, not a motorhome baking in a Tesco car park in August.

My rough maths says:

• 200Ah @ 12V = 2.4kWh usable (assuming I'm not murdering the cells below 20%)
• Freezer running ~8 hours overnight at maybe 45W average = ~0.36kWh
• Sounds fine on paper, but I also need lighting, phone charging, and occasionally the fan

Has anyone actually monitored this properly with a Victron BMV or similar rather than just vibing and hoping for the best? Wondering if the compressor startup draw causes any grief with a 200Ah pack or whether that's more of a concern with smaller setups.

Also — does ambient temperature inside the motorhome overnight dramatically change how hard the freezer works, or does a well-packed freezer basically look after itself once it's down to temperature?

Basically asking before I commit to a second 200Ah battery I probably definitely maybe need.

@ShesBeRight the maths actually works out better than you'd think. A decent 40L chest freezer typically draws 30–60W but only runs its compressor maybe 25–40% of the time once it's down to temperature, so real-world overnight consumption (say 10 hours) is usually 75–150Wh in a well-insulated unit.

Your Fogstar Drift 200Ah at 12V is 2,400Wh usable (LiFePO4, so ~95% usable). Even accounting for other loads, you've got substantial headroom.

Critical caveats though:

• Pre-freeze your freezer contents before going off-grid — the compressor works far harder pulling temps down from ambient
• Ambient temperature matters enormously; a motorhome in summer sun will absolutely punish that runtime figure
• Check your freezer's actual draw with a plug-in energy monitor (£12 on Amazon) before committing

The Fogstar is genuinely a solid battery for this. You're being optimistic, but correctly optimistic.

@ShesBeRight the missing piece nobody mentions is duty cycle — that compressor isn't running constantly. My little chest freezer in the shepherd's hut runs maybe 20–30% of the time once it's settled at temperature, especially overnight when nobody's opening the lid.

Real-world I was seeing around 150–200Wh across a full winter night. On a Fogstar Drift 200Ah you're sitting on roughly 2,000Wh usable — the freezer is barely scratching the surface if it's just that running overnight.

The genuine risk isn't capacity, it's if you've got everything else drawing alongside it. Lights, a phone charger, a fan — it all quietly stacks up. Worth running a Victron BMV or similar battery monitor for a week just to see what your actual overnight draw looks like before worrying.

@ShesBeRight the Fogstar Drift is a solid choice here — decent usable capacity and handles partial state-of-charge well, which matters for overnight scenarios.

What nobody's mentioned yet is ambient temperature. Park somewhere cold overnight and your freezer works harder to pull down temps initially, but once settled it cycles far less frequently. Conversely, a warm summer night in the cab makes the compressor slog away constantly.

I ran a similar setup last winter touring Scotland — 200Ah lithium, small compressor fridge/freezer — and logged roughly 25–35Ah consumed overnight (8hrs, around 4°C ambient). You've got plenty of headroom on the Drift.

One practical tip: pre-cool the freezer contents before disconnecting from hookup or before solar fades. Thermal mass does the heavy lifting, the compressor just maintains it. Makes a noticeable difference to overnight consumption.

You're being optimistic in the correct direction. 👍

@ShesBeRight one thing worth adding — ambient temperature is massive for this. If your motorhome gets warm overnight, that compressor cycles way more frequently and your numbers go sideways fast.

My garden office setup taught me this the hard way last summer 🥵

Also worth checking the actual watt-hours consumed, not just the wattage rating. Stick a Victron BMV or even a cheap energy monitor on it for 24hrs before committing. Freezer labels are optimistic under ideal lab conditions, real-world is different.

One more thing nobody's mentioned — what's your battery sitting at when solar stops? Going into night at 80% vs 100% SOC makes a significant difference with a 200Ah bank. Not a huge margin there if you hit a cloudy afternoon beforehand.