According to Wirecutter testing and The Solar Lab analysis, real-world usable capacity is consistently 10–20% below sticker specifications. Three independent loss factors compound: inverter efficiency losses (typically 85–90%, meaning 10–15% of stored energy is lost as heat during DC-to-AC conversion), idle consumption (the unit drains its own battery just by being powered on, even with nothing plugged in), and voltage sag under heavy loads.
According to The Solar Lab's video "We Tested 100 Power Stations," an entire chapter is dedicated to idle consumption — the phenomenon where some units consume 10–30 watts per hour just to keep their own electronics running. Over 24 hours, idle consumption alone can drain 240–720 Wh from a unit rated at 1,000 Wh.
According to Wirecutter testing, the EcoFlow Delta 2 (rated at 1,024 Wh) underperformed relative to its sticker specification. The pattern is consistent across brands: marketing communicates the raw cell capacity, not the capacity available at the AC outlet after all system losses.
"The box says 1,024 Wh. After inverter losses and idle drain, I'm getting maybe 850 Wh to my appliances. That's a 17% gap they don't advertise."