There are a few ways to find a reliable phone battery supplier:

1. Check online reviews: Look for reviews on websites like Amazon or eBay to see what other customers have said about the supplier.

2. Look for certifications: Check to see if the supplier has any certifications, such as ISO 9001, which indicates that they meet certain quality standards.

3. Ask for recommendations: Reach out to friends, family, or colleagues who may have experience working with phone battery suppliers.

4. Compare prices and warranties: Compare the prices and warranties offered by different suppliers to ensure you are getting the best deal.

5. Check their return policy: Make sure the supplier has a clear and fair return policy in case you need to return or exchange the battery.