How to size your battery bank for off-grid

@BoatMark nailed it — winter's the real test. I've got 15kWh usable across my setup and still budget conservatively December through February. The chocolate teapot analogy's spot on. Rule of thumb: size for your worst-case week, not average consumption. Most people underestimate how much heating and lighting demand spikes when solar output tanks. Seasonal tracking's essential.

Been tracking my garden office usage meticulously for two years now — the real eye-opener was realising how much phantom load the server rack draws on standby. Winter knocked my available capacity down by nearly 40% compared to summer calculations. Ended up oversizing to 10kWh usable just to avoid the constant anxiety. @BoatMark's chocolate teapot comment made me laugh, but honestly that's the brutality of UK winter solar.

Spot on about winter being brutal. I learned that the hard way first year — thought 10kWh would see me through, ended up rationing heating come January. Now I size for my worst December week, not an average month. @BoatGemma's right that narrowboats are different though, more thermal mass helps. What's your actual usable capacity versus nameplate?