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

Ran into exactly this last summer touring the Cairngorms. My Fogstar Drift 100Ah paired with a 50L Alpicool was fine during the day with panels topping things up, but overnight was a different story — woke up to 18% SoC more than once.

Few things that made a real difference for me:

• Raising the fridge temperature slightly — I'd had it set unnecessarily cold. Going from 4°C to 7°C dropped the compressor duty cycle noticeably
• Pre-cooling the fridge before disconnecting from hookup or shore power
• Insulating around the fridge — I stuffed a couple of old sleeping bags either side and it genuinely helped

The honest truth though? 100Ah is probably undersized if you're running a compressor fridge as your only significant load and expecting it to last a full 8-hour night with any buffer remaining. My Victron BMV-712 showed the fridge pulling around 3-4A average — that's 24-32Ah for an eight-hour night, which sounds fine until you factor in the Victron Cerbo keeping watch, a few USB charges, maybe some lighting...

It stacks up faster than you'd think.

I eventually added a second Fogstar 100Ah in parallel and the anxiety completely disappeared. Not cheap, obviously, but neither is getting stranded somewhere remote with a warm fridge full of food.

What fridge are you running and what's your panel setup? Sometimes there's a settings tweak that buys you enough headroom without needing new kit.

@VickyFisher welcome to the forum, good to have you here — and cracking choice of touring ground, the Cairngorms is brilliant.

Right, the maths is pretty unforgiving on this one. A 100Ah lithium gives you roughly 80-85Ah usable if you're being sensible with it. A 50L compressor fridge can pull anywhere from 30-50Ah overnight depending on ambient temp — and up in Scotland, temperature swings can actually work against you oddly, cycling the compressor more.

Few things worth checking:

• Fridge thermostat setting — people run them far colder than needed
• Ventilation around the unit — poor airflow kills efficiency
• Parasitic loads — what else is drawing overnight?

On my narrowboat I run a similar setup and a second 100Ah in parallel made an enormous difference. Fogstar Drift cells are solid, so the battery isn't your weak point here.

Same boat last year with a 100Ah Fogstar on a 60L compressor fridge. The overnight drain was killing me until I realised the fridge was working way harder than it needed to — ambient temp in the van was creeping up after sunset because I'd been cooking inside all evening.

Insulating the fridge properly made a massive difference. Threw a couple of old sleeping bag offcuts around the sides and top, not blocking the vents obviously. Dropped the compressor duty cycle noticeably.

Also worth checking your low voltage cutoff settings — mine was set too conservatively and was tripping before the battery was actually flat, so I was losing usable capacity I didn't know I had.

Realistically though, one 100Ah overnight with a compressor fridge is tight. Two batteries is the proper fix if you're doing extended trips.

@VickyFisher a 50L Alpicool typically draws around 30–45Ah overnight depending on ambient temperature — so a 100Ah lithium at 80% usable depth gives you roughly 80Ah, which is tight at best.

A few things worth checking:

• Thermostat setpoint — even 1°C warmer makes a meaningful difference to compressor duty cycle
• Ventilation around the fridge — trapped heat forces it to work harder
• Pre-cooling at home before you leave, so it's not fighting to pull down temperature overnight

Longer term, honestly a second 100Ah in parallel is the proper fix. Fogstar Drift cells are well-priced and their BMS handles parallel setups without fuss. I run two 100Ah units on my narrowboat with a 60L compressor and it's comfortably managed without touching solar overnight down to around 5°C ambient.

The Cairngorms in summer can still get properly cold at altitude, which won't help your duty cycle either.

@VickyFisher worth checking what your Alpicool's actual duty cycle is doing in those overnight conditions — the Cairngorms can get properly chilly even in summer, which should help the fridge run less frequently, but if your ambient inside the van stays warm it'll work harder than you'd expect.

I've got a similar situation with my static caravan setup and a 200Ah Fogstar Drift — even with double the capacity I was surprised how much the fridge was pulling on warmer nights.

Have you tried pre-cooling the fridge aggressively before sunset while your panels are still contributing? I found dropping the setpoint right down during the afternoon hours made a noticeable difference to overnight draw. What's your Alpicool set to temperature-wise? Some people run theirs colder than they actually need to.

@VickyFisher the Cairngorms ambient temps actually work in your favour for compressor efficiency — the fridge doesn't cycle as hard. The real culprit with 100Ah setups is usually the usable capacity ceiling people set on their BMS. Fogstar Drift units ship with conservative defaults; if yours is cutting out at 80% DoD you're effectively working with 80Ah, which after overnight parasitic loads (inverter standby, control units, 12V sockets) can shrink alarmingly fast.

On my van build I run a 200Ah Fogstar alongside a 60L compressor and log everything through a Victron SmartShunt — the overnight consumption data genuinely surprised me until I audited every standby draw. Worth installing a shunt if you haven't already; flying blind on a 100Ah bank with a compressor fridge is exactly why people wake up to flat batteries.