"New" batteries for this model are often old stock that may have degraded even while unused.
If you plan to install it yourself, you will need specific tools often sold in "Fix Kits": buy iphone 4 battery locally
A successful swap can restore the phone's ability to hold a charge for basic tasks like music or nostalgia, sometimes lasting up to 2 days on standby. How To: Replace the iPhone 4's Battery in 2 Minutes "New" batteries for this model are often old
National or local battery specialty stores often carry "compatible" versions for older models. ⚠️ Critical Purchase Considerations buy iphone 4 battery locally
Check small electronics repair kiosks in local malls.
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.