Given the size of 9cm x 4cm I can only suggest you check your countries resources online.
Where did you get the phone. I imagine the cost of returning the phone for a repair hasn’t seemed reasonable due to cost but have you asked officially if they will ‘repair the phone’ though you cannot send it back with a damaged battery.
EDIT 1
How old is the phone, please read
EDIT 2
If the battery is not within warranty which I think is a year for the battery check out the cost as a repair