I bought the same BB Toshiba laptop.
The manual clearly said that leaving the battery with the power plug in
will worsen the battery life in the long run.
Constantly charging the battery @ its maximum potential over a long period of time,
compromise the battery ability to give accurate reading on its power-level....etc....
I don't know if Toshiba is extraggerating, but I"m keeping mine off till I heard a more
scientific explanation of either direction.