It has 2 internal batteries, and with older batteries, they can fail to switch from one to the other when they reach 0%. Models with a removable battery are a bit bulkier, but I think of greater value.
I've got a $150 T480s. It only has one, non hot swappable battery. Though it can be easily replaced. The T480 non s has 2 batteries. One external and one internal. Unless you count the cmos battery, which can be replaced on either. The build quality on the T480s is also higher.
