Eh... I have a T480. It's advertised at "17+" hours. With the 72Wh extended battery fitted, it has a total of 96Wh energy storage. With some small effort tuning (making sure the nvidia GPU is properly powered down etc) I can easily get its consumption down to about 5W - less, with lowered screen brightness and wifi off. 96Wh / 5W = 19h 12 min. Seems legit.