Welcome to the Small Repair Forum, where we discuss repairability and DIY of common repairs.
One of the challenges with DIY repair or getting your phone fixed from the local mobile repair shop, is the lack of original spare parts from the manufacturer.
Almost 100% of the spare parts available outside the service network, are 3rd party products with no valid warranty. This is especially a problem for batteries, since it is one of the most common parts which needs to be replaced.
A quick search for your particular battery model will show several retailers who offer it for sale, however the quality of most of them will be questionable. A great video on this topic is below: