The Power Nobody Uses

When people build a load list, almost everyone writes down the appliances that switch on: lights, air conditioning, fridge, television. What actually eats the battery is the set that never switches off — inverter idle draw, router, set-top box, smoke alarm, access control, air conditioner standby, water heater control board. Each is small on its own, but each is multiplied by twenty-four hours.
 Measured ranges run roughly like this: inverter idle 10–30 W (240–720 Wh a day), router and modem 10–20 W (240–480 Wh), set-top box standby 8–15 W with field readings up to 30 W, television standby 1–5 W, microwave clock 2–7 W. Together a typical home carries 40–60 W continuously, which is 1.0–1.5 kWh a day. Berkeley Lab's rule of thumb is that one watt running all year is about 9 kWh. An NRDC analysis of 70,000 smart meters went further: average always-on load of 164 W, 23 percent of those households' electricity.
 Put that on a cabin: with a daily budget of 2–3 kWh, always-on loads take a third to a half. There is also an amplification effect people miss. Inverter efficiency collapses at very light load — 55–70 percent at 2 percent of rated output, against 90–95 percent in the 30–70 percent band. Running a 3 kW inverter to carry 50 W overnight turns a good share of the energy into heat inside the box. The fix is a 300–600 W secondary inverter for night loads, or a unit with a genuine eco mode, rather than leaving the big machine idling.