Battery Low Samsung Mega 6.3 i9200 battery charges slow

Hi guys...being new here.

I thank XDA Developers for accepting me as a part of this largest mobile community on Earth.

I have been using Samasung Galaxy Mega 6.3 i9200 for the past 3 months. Everything worked seamlessly until the battery issue that popped up a week ago.

It takes over 9 hours to get charged up fully. Before it took just 1 n half hour to reach 90%.

Any idea what could be the problem? Replacement of the battery or an internal issue?