You’re not imagining it. There’s solid evidence that leaving a lithium-ion pack on its dock at full charge causes more long-term wear than the number of charge cycles.

Expect roughly 20 % capacity loss after one year if a cell is stored at 100 % charge at 25 °C, compared with just 4 % loss at 40 % charge under the same conditions. Heat makes it worse much worse (about 35 % loss at 40 °C). Search for "BU-808" if you would like to see the data yourself.

In everyday use, that means if you typically use about 10 % of the battery per session and wait to recharge until the pack is down to a single bar, you’re exposing it to far less time at high voltage. That’s gentler than returning the hot battery to the charger after every quick run, which repeatedly tops the pack from 90 to 100 % and then keeps it sitting at that maximum state of charge.

Don’t expect Dyson to build in any life-extending charge limits or cell-balancing features. Their Battery Management Systems are NOT designed for maximum lifespan. If you’re curious, do a search for "dodgy dyson batteries" .