Hi @shivamshar14684
Here's the [https://downloadcenter.samsung.com/content/UM/201505/20150529144537542/GT-I9300I_UM_Open_HongKong_Kitkat_Eng_Rev.1.0_140807.pdf|user manual] for the phone.
Go to p.10→ p.12 to see how to insert/remove the battery from the phone.
If you need a new battery, search online for [https://www.google.com/search?client=firefox-b-d&q=eb-l1g6lla|EB-L1G6LLA] to find battery suppliers that suit you best (supplier examples only)