As Jason wrote, when you add a new state the way you did (by using a string value to set the state) this state will be added at the next available number in the state profile. By default, a task executer has 22 states (up to "busy"). Since you apparently already used "waiting", the states up to that were added to the TE along side it, so your TE had 49 states in its profile.
As such, the new "Charging" state was added as the 50th state.

The Statistics Collectors that deal with states only use the numerical value from the profile. The name is taken from the connected State Table. The State Table in your model uses the defautl arrangement in which state 50 (the last default state) is called "Accumulating".

Again, as Jason already said, change the display name in the State Table to your desired value to have it show up in the chart.