How long will 200Ah last running a 12V fridge?

Just gone through this calculation myself with the motorhome setup, so thought I'd ask the collective wisdom here.

I've got a 200Ah LiFePO4 bank (Fogstar cells) running a 12V Dometic fridge in the van. Looking at the specs, the fridge pulls roughly 4-5A when the compressor's actually running, but obviously it cycles on and off depending on ambient temperature and how often you're opening it.

My question is: what's a realistic timeframe I should expect before needing to recharge? I'm planning a week away in autumn where I won't have solar or hook-up, just the battery bank and a small generator for emergencies.

I've seen wildly different figures online—some say you'd get 40 hours, others claim much longer. Suspect it depends heavily on:

• How efficient your fridge actually is
• Ambient temperature (mine will be in a cold Scottish cabin)
• How much you're raiding it

I'm running a Victron BMV-712 to monitor consumption, but haven't had the fridge long enough to gather real-world data across different seasons.

Should I be provisioning for the generator by day 4-5, or am I being pessimistic? Also curious if anyone's actually measured their 12V fridge draw under real conditions rather than just going by specs.

Cheers all.

Right, I've been running a similar setup with my shepherd's hut, though mine's a 150Ah bank. The Dometic will draw roughly 3-5A depending on ambient temp and how often the door opens—summer's brutal for this.

Quick maths: you're looking at 40-65 hours of runtime on a full 200Ah, but that's theoretical. In practice, you won't want to drop below 20% state of charge on LiFePO4, so you're really working with about 160Ah usable. More like 30-50 hours realistically.

Where I learned this the hard way was last July—left the fridge running without adequate solar input for three days. The ambient heat absolutely hammers consumption. If you're stationary with decent irradiance, a 400W panel sorts it. On the boat, I added a small dedicated panel just for the fridge circuit.

What's your solar setup looking like? That's the real limiting factor, not the battery capacity.

Depends massively on ambient temps and how often you're opening it. My 200Ah Fogstar setup runs a 12V Dometic, and I'm seeing roughly 30-40A draw when the compressor kicks in, but it cycles on/off.

Rule of thumb: assume 60-80 amp-hours per day in summer, maybe 40-50 in winter. So you're looking at 3-5 days comfortably, though that assumes you're not draining below 20% DoD on LiFePO4 (which you shouldn't be).

Real talk though — what's your actual fridge model? The newer Dometics are more efficient than the older ones. Also matters if you've got decent insulation around it.

@ExFirefighter11 spot on about the shepherd's hut difference. Mobile setup gets warmer in summer than static caravans imo.

Real world - that 200Ah won't get you as far as the specs suggest. Friidge draw varies wildly depending on ambient temp, insulation, and how often the compressor cycles.

I've got a similar Fogstar 200Ah setup powering a 12V Dometic in my cabin. Summer months, if it's hot outside, you're looking at maybe 3-4 days before you'd want to top up. Winter, closer to a week. The thing is, you don't want to regularly discharge below 20% on LiFePO4 anyway - kills longevity.

Key factors:

• Ambient temperature makes the biggest difference. Heat = compressor runs constantly
• How full the fridge is - more thermal mass keeps it cooler longer
• Door openings - obvious but worth stating

If you're relying solely on battery without solar/wind to keep topping up, 200Ah is tight for a fridge as your only load. Even modest solar (400W panel minimum) makes a real difference. Are you planning renewable generation alongside the battery, or is this for occasional use?

Mate, the real killer is whether you're in summer or winter — my Dometic pulls about 40A starting current then settles to 8-12A running, but in July it's basically a tiny air conditioning unit. With 200Ah usable you're looking at roughly 16-25 hours in mild conditions, half that if it's roasting.

The Fogstar cells handle it brilliantly though — they don't sulk about the duty cycle like lead-acid would. I'd say don't rely on more than 80% depth of discharge if you want them lasting beyond a decade. Factor in your solar recharge rate too, otherwise you're just slowly mining your bank.

@SaltyHiker's spot on about opening it constantly being the real energy vampire.

Good question — I'd actually challenge the starting current figures a bit though. My experience with the same Dometic in the van is that you're looking at more like 25-35A peak depending on compressor condition, then 5-15A steady state once it's running.

The real variable I've found is how efficiently your fridge is actually working. Mine was drawing way more than expected until I realised the door seal was dodgy — sorted that and consumption dropped noticeably.

With 200Ah usable (assuming you're not going below 20% on LiFePO4), you're working with roughly 160Ah realistically. In summer I'm seeing the fridge cycle every 20-30 mins for maybe 10 mins each time. That's ballpark 4-6 days without any solar input, but obviously depends on your ambient temps and how much the door's getting opened.

What's your van setup like temperature-wise? Are you insulated well, and what's your ambient temps looking like where you are?

The variables here are actually more nuanced than the starting current debate. What matters is the duty cycle — how often the compressor kicks in.

I've got a similar setup in the shepherds hut with a Fogstar 200Ah bank and a 12V Dometic. In summer, ambient temp being higher means the fridge runs constantly at roughly 3-5A draw between compressor cycles. That'll drain your bank in 40-50 hours if you're not generating.

Winter's actually your friend — the compressor might only run 30-40% of the time, so you're looking at 60-80 hours comfortably.

The real variable @SaltyHiker's hinting at: usable capacity. You shouldn't discharge LiFePO4 below 10-15% for longevity, so your effective bank is closer to 170Ah. That changes the maths considerably.

Also factor in whether you've got solar topping it up daily. If you're relying purely on the bank without generation, you're looking at 2-3 days maximum in summer, longer in

Right, so everyone's dancing around the real answer — it completely depends on your fridge's compressor duty cycle, which varies mad amounts based on ambient temp, how often you crack the door open, and whether you've actually insulated the van properly or it's just a glorified oven.

My Dometic in the shepherd's hut pulls roughly 3-5A continuous when running, but only cycles maybe 30-40% of the time. That gives you roughly 120-200 hours before you're properly knackered, assuming decent conditions. Summer? You're looking at the lower end. Winter? Closer to 200.

@SolarKeith's starting current point is valid but honestly irrelevant here — that's a millisecond spike. The real drain is the sustained runtime.

Proper answer: stick a clamp meter on it for 24 hours in your actual setup and you'll know precisely. Beats forum guessing every time.

Has anyone factored in ambient temperature? Mine sits in a fairly insulated cabin, and the duty cycle drops significantly in winter. Also curious if you're measuring actual draw with a clamp meter — Dometics can vary wildly depending on age and condition. What's your typical daily usage pattern?