Wharfedale portable DVD gone bang & cloud of smoke?

Through a series of circumstances, my daughter's Wharfedale portable DVD -266 was connected to mains power, through a converter, but on the wrong polarity. i.e. -ve to +ve rather than +ve to +ve. Whereupon, there was a bang and a lot of smoke and it stopped working (understandably).

Does anyone know if this is fixable ? Could it be that just the battery has been damaged and a new battery would do it ? It has an internal battery and also a big flat battery which attaches to the base and which was in place at the time of the disaster.

Help would be greatly appreciated, my daughter saved for months for this machine and it was the best thing she ever had....