Help for headphones repair

The battery of my Anker Q20i headphones (over ear) is draining way to fast since a month or so. like going from 100 to 50 in 30-45 mins when it used to last me whole day and more on one charge.

warranty period is over so no help from the original company.

please suggest me what I can do about this and also of there is a trustworthy shop in surat where I can get them repaired if I have to.