I'm not super-knowledgeable on this but as far as I understand it, they improve battery lifetime significantly by having low per-cell draw, not running the batt

I'm not super-knowledgeable on this but as far as I understand it, they improve battery lifetime significantly by having low per-cell draw, not running the batteries all the way down or charging them all the way up, and having a fancy cooling setup to prevent cells getting too hot. They still degrade noticeably, but at a slower rate than your typical portable device (where the relevant marketing metric is battery life from a full charge down to zero, rather than battery longevity).