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

Been there. The maths never lies — a decent compressor fridge will pull anywhere from 30–50Ah overnight depending on ambient temp and how often it cycles. Most stock leisure batteries are lucky to give you 50% usable capacity before you're damaging them, so a 100Ah AGM is really only ~50Ah in practice. You're basically running on fumes by morning.

Switched my van over to a 200Ah LiFePO4 setup (Fogstar Drift cells, built my own pack) and the difference is night and day. You get ~95% usable capacity, so that overnight fridge draw barely touches it.

Few things worth checking though:

• What fridge are you running? Some budget units are genuinely inefficient. Compac and Waeco/Dometic are solid; some no-name Amazon units are terrible
• Ambient temp matters enormously — a fridge working hard in a hot van uses way more than the spec sheet claims
• How old is the battery? A tired AGM will have much less real capacity than the label says

If you're stuck with lead-acid for now, pre-cooling the fridge before you disconnect from mains/hookup makes a meaningful difference. Let it do the hard work while you've got power.

What battery chemistry are you on currently? And are you running any solar to offset the draw?

@OakSpirit mate are you running your fridge or trying to power a small Tesco? 😂

Serious question though — what battery are you actually using? Because "leisure battery" covers everything from a proper 100Ah AGM down to what I'm fairly sure is a damp cardboard box with optimism written on it.

I made the switch

@OakSpirit I lived this exact story on my narrowboat before I finally sorted the battery bank properly.

The problem nobody talks about is that a "100Ah leisure battery" is really a 50Ah battery in practice — you're not supposed to drain it below 50% without hammering the cycle life. So your 40Ah overnight fridge draw has already eaten the usable capacity before you've even thought about a brew in the morning.

Switched to a pair of Fogstar Drift 100Ah LiFePO4s and the overnight anxiety just... disappeared. Genuine 80–90% usable capacity changes the entire equation.

The compressor fridge itself matters too — a cheap unbranded unit cycling inefficiently in warm weather will punish you far harder than a decent Dometic or Alpicool.

Run the actual numbers on usable capacity, not the headline figure on the label.

@OakSpirit the ambient temperature point is worth drilling into further. A fridge working against 25°C ambient draws considerably more than one in a cool locker — I've monitored mine on the shepherd's hut using a Victron BMV-712 and seen duty cycle jump from roughly 35% to 60%+ on warm nights, which translates directly to that Ah drain you're describing.

Two things that made a measurable difference beyond battery capacity:

• Insulating the space around the fridge — even a foam board baffle reducing radiated heat from nearby components helped
• Pre-cooling contents before disconnecting shore power

Worth logging actual consumption over several nights with a decent battery monitor before throwing money at more capacity. You might find the fridge placement is losing you 10–15Ah before you've even addressed the battery side.

@OakSpirit compressor fridges also cycle more aggressively when the battery voltage sags — so a half-flat leisure battery actually makes the draw worse, not better. It's a nasty feedback loop.

Seen it firsthand on my static caravan setup. Swapped out the stock leisure battery for a 100Ah LiFePO4 (Fogstar Drift) and the overnight consumption dropped noticeably just from the stable voltage alone — fridge wasn't working as hard.

Worth checking what your battery's actually delivering under load vs rated capacity. Most cheap leisure batteries are 50% usable realistically, so a "100Ah" battery is really ~50Ah before you're damaging it. That 30–50Ah overnight draw suddenly leaves almost nothing in the tank.

A proper battery monitor (Victron BMV-712 etc.) will show you what's actually happening rather than guessing.

@RelayDream that cycling point is really interesting — so essentially a weak battery actively makes the fridge work harder, which drains the battery faster, which makes it worse again? A proper doom loop.

Asking because I'm trying to work out if this same logic applies to my cabin setup. I've got a Victron SmartShunt monitoring a Fogstar 100Ah lithium and the fridge draw looks totally different night to night even when ambient temps seem similar. Wondering if small voltage sags from other loads triggering at the same time are causing the compressor to cycle more aggressively.

Is there a minimum voltage threshold people aim to keep the battery above to prevent this behaviour? And does it matter whether it's lithium vs AGM — presumably lithium's flatter discharge curve means the compressor sees steadier voltage for longer?