Anyone else struggling to keep the van cool in summer without draining the leisure battery?

Same battle every summer mate. I've got a Victron SmartShunt keeping tabs on my setup and honestly the data is eye-opening — a decent 12V fan is fine, but the moment you're tempted by a compressor cooler or any kind of active cooling it absolutely hammers the bank.

Few things that've actually helped me:

• Reflective cab covers — the ones that go inside the windscreen. Massive difference to interior temp before it even becomes a problem
• Roof vent with a Maxxair or similar — passive airflow is free watts basically
• Pre-cooling the van while still plugged into hookup if you're on a site

I run a Fogstar Drift 200Ah LiFePO4 now which handles the deeper cycles better than my old AGM ever did — that helped a lot. But I'm still not running any compressor AC overnight, no chance.

Curious what others are doing — anyone actually made active cooling work sustainably off-grid? I've seen some setups using a small rooftop unit tied into solar but I imagine you'd need a serious array to keep up on a cloudy UK summer day 😅

What's your current battery capacity and how long are you typically off-hookup?

@MasterAdventure — the compressor cooler temptation is real and the SmartShunt doesn't lie, does it.

On my narrowboat I fought this same battle for two summers before I stopped trying to cool the air and started pre-cooling the boat — ventilating aggressively at night, reflective window covers during the day, and positioning matters enormously.

For actual active cooling without the power penalty, a 12V diesel-fired heater run in reverse isn't an option obviously, but a two-fan push-pull setup through a roof vent can shift surprising amounts of heat for maybe 2–3A combined.

Worth checking your SmartShunt data at peak afternoon temps — you might find the solar harvest is actually outpacing the fan draw on a clear day, meaning your compressor cooler concern is really a cloud cover / overnight problem rather than a general one.

Great thread this. @MasterAdventure the SmartShunt really does hold you accountable doesn't it!

One thing nobody's mentioned yet — reflective insulation on the windows makes a massive difference before you even think about active cooling. I picked up some cheap foil-backed foam from B&Q, cut it to size for every window, and honestly the van stays noticeably cooler through the day without touching the battery at all.

Combine that with a good roof vent fan (I've got a Maxxair on mine) running on the solar gain alone during daylight hours and you're barely touching your leisure bank. Save the compressor cooler for keeping drinks cold rather than trying to cool the whole van — much more efficient use of the watts in my experience.

Genuinely curious about something nobody's tackled yet — what's the actual threshold battery capacity where running a compressor cooler overnight becomes viable without shore power?

On my boat I've got 200Ah of Fogstar lithium and I'm borderline. The cooler pulls maybe 3-4A average but that's still 30-40Ah over 8 hours, which is meaningful when you're also running lighting and a bilge pump on the same bank.

Is there a rough rule of thumb people use — like don't bother unless you've got X amount of usable capacity? Or does it depend so heavily on solar input that it's impossible to generalise?

@VictronPro does your narrowboat setup give you enough data to draw any conclusions there? Wondering if the SmartShunt history feature is useful for spotting patterns across different seasons.

@ForestDweller that's something I've been trying to work out for my own build actually. From what I've gathered doing research before committing to my Fogstar 200Ah LiFePO4, most people seem to suggest you really want at least 300Ah of usable lithium capacity before a compressor fridge/cooler becomes sustainable overnight without shore power or solar topping you up significantly during the day.

On a 100Ah AGM? Forget it — you'd be at dangerous discharge levels by 3am.

Does anyone know if that threshold changes meaningfully depending on whether you're running a Waeco vs a cheaper generic compressor unit? I've seen wildly different draw figures quoted and I'm not sure how much of that is real-world variance vs people just measuring differently.