Battery problem in KTM RC8 1190

Hi guys,

A friend of mine has a KTM RC8 1190 that hasn't been started for quite some time. So now the bike is not starting, even after charging the battery to 100%. What might be the problem here?
Kindly share your experience if anyone has had the same problem in the past. Shoutout to all the superbike owners out here on xbhp. It will be a great help.

Thanks