Hi
Here’s a [https://www.youtube.com/watch?v=Wz6LBI7C9to|video] that shows how to replace the battery in your phone.
The battery can be seen being taken out from 2:40 minutes into the video.
Replacement batteries are available online. Just search for ''EB-BG610ABA'' to get results for suppliers that suit you best. (''verify the battery model number with what is printed on the battery in the phone before ordering'').
Ifixit has the [product|IF145-348-2] and [product|IF145-198-4] (click on Tool only) which will help with the repair