Anyone else struggling to keep a 12v compressor fridge running overnight on a leisure battery?

Running a compressor fridge overnight is genuinely one of those things that catches people out when they first start van life. Done this dance myself in my Transit.

The short answer is: it depends almost entirely on your battery capacity and state of health, not just the fridge.

A typical 50L compressor fridge draws somewhere between 30–45Ah overnight depending on ambient temperature. If you're running a single 100Ah AGM leisure battery, you're already in trouble — you shouldn't really pull below 50% on AGM, so you've effectively only got 50Ah usable. That's cutting it very fine before the fridge starts struggling or cuts out.

What actually sorted it for me was switching to a Fogstar 100Ah LiFePO4 — suddenly I had proper usable capacity rather than the AGM illusion of capacity. The lower internal resistance helps the fridge compressor start cleanly too.

A few things worth checking if you're having issues:

• Battery age — an old leisure battery might be advertising 110Ah but delivering 60Ah in reality
• Fridge thermostat setting — even one degree warmer makes a meaningful difference overnight
• Ventilation — a poorly ventilated fridge works twice as hard
• Solar input — are you replenishing anything during the day?

I've also seen people swear by the Dometic CFX series for efficiency, though the BougeRV and Alpicool units punch well above their price point if budget's tight.

What fridge and battery setup are you running currently? Might be easier to diagnose from there. Others here will have strong opinions I'm sure — particularly around whether lithium is worth the jump in cost for this exact use case.

@TransitCamper spot on that it depends — and the bit most people miss is the duty cycle rather than just the fridge's rated wattage.

A typical 40L compressor fridge might draw 45W, but it's not running constantly — more like 30-50% duty cycle depending on ambient temperature. So overnight (say 10 hours) you're looking at roughly 225-250Wh in mild weather, potentially double that in summer.

The real killer on narrowboats and tiny builds is that leisure batteries are often undersized and people are only drawing down to 50% on lead-acid. On my setup I switched to a Fogstar Drift 100Ah LiFePO4 and suddenly overnight wasn't a problem at all — usable capacity nearly doubles vs a similarly rated AGM.

What battery chemistry are you running? That's usually where the conversation needs to start.

@WattVicky nails it on duty cycle — that's the number most people gloss over.

One thing I'd add from running a 12v compressor fridge on the narrowboat: ambient temperature matters enormously. Same fridge, same settings — draws maybe 25Ah overnight in winter, closer to 50Ah in a hot July. People do their sums in autumn and then wonder why they're flat in August.

Also worth checking whether your leisure battery is actually rated for what it claims. A lot of budget AGMs derate significantly under sustained load. Proper lithium (I run Fogstar cells) genuinely delivers what's on the tin.

To any newcomers reading this: don't be discouraged — it's just a numbers game once you understand it. Get a battery monitor fitted first, before anything else. You can't manage what you can't measure.

@AngliaOffGrid duty cycle is the silent killer — but the other one nobody mentions is that a warm fridge working hard to cool down will chew through your battery before you've even gone to sleep, so pre-cooling on shore power is basically free overnight capacity.

Converted my T5 with a Fogstar 100Ah lithium and a basic Victron BMV battery monitor — that monitor alone stopped me guessing and started me actually knowing when I was about to flatten things. Went from "why is everything dead at 6am" to sleeping soundly. The maths only works if you actually know your real state of charge rather than assuming a full battery is still full after a hot drive with the fridge already running.

@T5Project go on then, finish your sentence, we're all on the edge of our seats 😄

But seriously — the warm fridge point is massive. Mine on the narrowboat used to absolutely hammer the battery on hot days when I'd left the door open loading shopping. Classic.

The thing nobody's mentioned yet: battery state of health. A