Been dealing with this exact headache across three builds now. The problem isn't just the cooling load itself — it's that peak demand hits exactly when you're stationary and not topping up from the alternator.
My current van setup runs a Webasto FCF off a 200Ah Fogstar lithium bank with a 300W Renogy panel on the roof. Honest answer: it's marginal on overcast days. One cloudy afternoon in Wales last July nearly had me running the engine just to keep the battery above 20%.
A few things that've genuinely helped:
- Reflective window covers (the proper thick ones, not the foil camping mats people bodge together) — makes a massive difference to the thermal load before you even think about active cooling
- Roof vent fans running on a timer overnight to flush cool air through — cheap and surprisingly effective
- Monitoring actual consumption via a Victron SmartShunt rather than guessing — you'd be amazed how many people don't know what their setup is actually drawing
The uncomfortable truth is that most 12V compressor coolers and certainly any vapour-cycle air conditioning will overwhelm a typical 100-200Ah setup in sustained hot weather unless you've got serious panel capacity or a DC-DC charger keeping things topped from the engine.
What's everyone actually running capacity-wise? I'm wondering whether the 400Ah+ brigade are genuinely comfortable or just buying themselves an extra few hours of anxiety.
