To remove the internal battery connector screw.
National or local battery specialty stores often carry "compatible" versions for older models. ⚠️ Critical Purchase Considerations
Stores that focus on vintage electronics or legacy device repairs.
Ensure you buy a battery specifically for the iPhone 4 . The iPhone 4S battery has a connector on the opposite side and is not compatible.
If you plan to install it yourself, you will need specific tools often sold in "Fix Kits":