What are the horizontal lines under the battery level graph?

[barbsuenet]

 

[gwang73]

It shows you a little more info like when it's charging or charging has been paused.

 

[raythompsontn]

The lines show when the device was connected to a charging source and charging. Notice that the battery level lines get taller at the same time the horizontal lines appear. The device stopped at about 80% until the OS has determined that you normally start using the device and completed the charging to 100%.