Hi,
Easiest way to distinguish if it's the battery or the AC Adapter is to swap both AC Adapter and battery with the other Toshiba laptop since you have 2 of them.
- First use the charger from the other laptop(working) to the one who's having problem.
- Second is to try the AC Adapter from the non working laptop to other working laptop and see if it does the same thing.
- Contact the manufacturer right away if it's the AC adapter as it may need a replacement if the same problem persist in the other working laptop.