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

Mate, a single leisure battery trying to run a compressor fridge overnight is basically just a very expensive way to have warm beer by morning. 🍺

Been there with my shepherd's hut build — the fridge alone was murdering my battery by about 3am, and I hadn't even accounted for the control board ticking away in the background.

Here's what actually sorted it for me:

• Went to 200Ah of lithium (Fogstar Drift cells — properly good value for UK buyers)
• Added a Victron SmartShunt so I could actually see what the greedy little fridge was pulling rather than just guessing
• Insulated the fridge cabinet properly — made a surprisingly big difference to compressor cycle frequency

The real villain is usually ambient temperature. A fridge working hard in a warm van on a summer night will absolutely flatten a single 100Ah AGM before sunrise. Physics is ruthless like that.

If lithium isn't in the budget yet, the cheapest win is genuinely just pre-cooling everything before you switch to battery power — warm food going into the fridge is basically asking it to run flat out all night.

What fridge are you running? Some of the cheaper Renogy and no-name units are significantly less efficient than a Dometic or Indel B — the upfront cost difference often pays back fairly quickly in battery longevity alone.

Anyone else found a particular fridge brand surprisingly efficient? Always keen to compare notes.

Midge55 | 847 posts

@OffGridHamish Ha, warm beer and a flat battery — the classic off-grid double disaster! 😄

The maths just don't lie with these fridges. A decent compressor unit pulls anywhere from 3-5 amps average over 24 hours depending on ambient temp, so you're looking at 72-120Ah daily. A standard 100Ah leisure battery has maybe 50Ah usable before you're damaging it. Something's got to give.

Few things that genuinely helped me:

• Adding a second battery in parallel (obvious but transformative)
• Insulating around the fridge, not just relying on its own insulation
• Keeping it out of direct sunlight

The ambient temperature thing is massively underrated — a fridge working in a 30°C van is a completely different beast to one in a cool cupboard.

What's your current setup for charging? Solar, split charge, or both?

CopperWelder | 1,203 posts

@OffGridHamish Ah yes, the Single Leisure Battery Optimism Phase — we've all been through it. Right between "how hard can it be?" and "why is everything beeping at 3am?"

My shepherd's hut went through three iterations before I accepted the maths. A typical 12v compressor fridge pulls 4-5Ah average overnight — sounds manageable until you factor in that your 100Ah battery is really ~50Ah usable (unless you fancy replacing it annually). That's your entire overnight budget gone before you've even considered lighting.

Minimum viable solution in my experience: two batteries, properly wired in parallel, and a decent battery monitor — I used a Victron BMV-712 and suddenly realised I'd been lying to myself about state-of-charge for months. Add solar if you can. The fridge problem doesn't really get solved; it gets outgunned.

RetiredSquaddie | 2,341 posts

@OffGridHamish The maths simply don't lie here. A typical compressor fridge like a Dometic CFX-35 pulls around 45Ah per 24hrs in moderate ambient temps. A 100Ah lead-acid leisure battery is realistically only 50Ah usable before you're damaging it. You've already lost before sunset.

Minimum viable setup in my experience:

• 200Ah LiFePO4 (Fogstar Drift cells are decent value)
• BMS with proper low-temp cutoff
• At least 200W solar to recover daytime losses

I run a 12V Alpicool on my rig with a 280Ah lithium bank — fridge barely registers overnight. The compressor duty cycle drops dramatically once it reaches target temp, so those peak current figures are misleading if you're panicking at the spec sheet.

Lead-acid and compressor fridges are genuinely a poor combination. Lithium changed everything for this specific use case.

BitsAndBobs | 412 posts

@OffGridHamish Two Fogstar Drift 100Ah lithiums under the bed of my van later, and suddenly my Dometic is purring away like it's got nothing to worry about — funny how that works. 🔋

The real villain nobody mentions is ambient temperature; park your van in a sunny field in August and even a decent bank will weep quietly to itself by 3am. Throw a bit of shade or insulation around the fridge cabinet and you'll shave a surprising chunk off the draw. Sorted mine with a bit of leftover van lining foam and some cable ties — proper Blue Peter energy.