Anyone else struggling to keep the compressor fridge running overnight on a 100Ah lithium?

Had this exact issue at the cabin last summer. Compressor fridges are great but they're sneaky power hogs — mine was pulling around 4-5A on average once you factor in the duty cycle, so overnight (say 10 hours) that's 40-50Ah gone before you've even thought about lighting or charging your phone.

With a 100Ah lithium you've only really got 80Ah usable if you're being sensible about it, so yeah, it's tight.

Few things that helped me:

• Pre-cool the fridge before the sun goes down while you've still got solar input
• Check the ambient temp — these compressors work much harder in a warm van
• Make sure the fridge has decent airflow around it, mine was tucked in a cupboard which was killing efficiency
• Fogstar do decent 100Ah cells if you're thinking of adding a second battery, the prices are reasonable

Honestly though, if you're running just the one 100Ah and you've got a decent solar setup, you might be fine in summer but winter's a different story. I ended up going to 200Ah and it made a massive difference — no more morning anxiety checking the battery levels.

What fridge are you running? Some of the cheaper compressor units are nowhere near as efficient as a Dometic or a Brass Monkey. That alone could be your problem.

What's your solar setup like too? Might be worth sharing the full picture so people can give proper advice.

@Chopper your maths is roughly right but the devil's in the detail. A 100Ah lithium at 50% usable (if you're being cautious) gives you ~50Ah overnight. At 4-5A average draw that's only 10-12 hours before you're in trouble — tight for a full night.

Few things that helped my setup:

• Ambient temperature matters enormously. Fridge works harder in a warm van
• Pre-cool the fridge contents before you leave home
• Check your fridge thermostat setpoint — many people run them colder than necessary
• Victron BMV-712 will show you actual average draw rather than guessing

Honestly though, 100Ah is undersized for a compressor fridge as your only load if you're not charging during the day. I'd consider either a second battery or a small solar top-up even just 100W will meaningfully extend your overnight capacity.

On a boat I've learned the hard way that ambient temp makes a massive difference to duty cycle. Same fridge in summer vs a cool spring night is almost double the draw.

Worth checking what your fridge is actually pulling with a proper meter — I use a Victron SmartShunt and the real-time data is eye-opening. Most people are surprised how much worse it gets when the compressor's working against a warm cabinet or direct sun.

If you're consistently struggling overnight, a bit of extra insulation around the fridge casing helps more than you'd think. Cheap fix before throwing more panels or battery at it.

@BazBurns raises a crucial point that often gets overlooked — insulation quality is equally significant. On my narrowboat, I lined the fridge cavity with 25mm Celotex and the duty cycle dropped noticeably. Worth doing before throwing battery capacity at the problem.

The other variable nobody's mentioned: starting surge. Compressor fridges can pull 3-4x their running current on startup, which matters if your BMS has conservative overcurrent limits. Fogstar Drift cells handle this fine, but I've seen cheaper lithium packs trip out repeatedly on older Renogy batteries with tight BMS thresholds.

If you're consistently running overnight on 100Ah, I'd also look at your charge input — are you actually recovering that energy the following day? A Victron BMV-712 will tell you exactly what's going in versus out, removing the guesswork entirely.

@DefenderAdventure all valid points but nobody's mentioned the obvious — pre-chill your food before it goes in the fridge, not after, saves your battery doing the heavy lifting from warm. My shepherd's hut setup runs a Fogstar 100Ah with a Brass Monkey 40L compressor and I lose maybe 15% overnight just because I'm not lobbing room-temp milk in at 10pm like an animal. Also worth checking your Victron BMV if you've got one — half the time people think it's a battery problem and it turns out the fridge vent's blocked and the compressor's working twice as hard.

@ExFarmer79 has got the pre-chilling sorted but nobody's mentioned the actual maths — 100Ah lithium (usable ~80Ah if you're being sensible with your Victron BMV) versus a 4-5A average draw is barely 16 hours before you're in the danger zone, and that's assuming your fridge isn't working overtime because someone left the door open for 30 seconds deciding what to eat.

My static caravan setup runs a dedicated 200Ah Fogstar battery just for the fridge — problem solved, everyone else arguing on forums whilst I'm drinking cold beer.

If budget's tight, even a basic Renogy DC-DC charger to top up from vehicle alternator whilst driving buys you headroom overnight. Separate your fridge circuit from everything else and thank me later.