Chris Same problem with NP 2a , with SAMSUNG 45 watt charger.
sent multiple mails to support team , gave few tips , factory reset etc. then went to service centre- not useful.
for 3 months it was fantastically charging , thwn problem started, but every time i restart ,it worked fine but after some time ,it shows charging rapidly without charger plugging in , and when i plug in the chager it is not charging.
they have to fix it via software update.