A website called mendmyi, which replaces batteries in iPhone 5’s, has discovered that your phone is not holding charge due to third-party charging cables.
Apple announces a replacement program for some European iPhone USB adapters that may overheat and pose a safety risk. The adapters shipped with European models of iPhone 3GS, iPhone 4 and iPhone 4s from October 2009 to September 2012.
Apple lauched a USB Power Adapter takeback program last year to help costumers replace their counterfeit chargers with Apple chargers, Apple did this due to a few deaths that occurred because of these fake chargers.
You can buy an iPad charger for $19 at Apple Retail and Online stores, while the counterfeit chargers are only a couple of bucks on eBay. Ken Shirriff has written a post on his blog about how dangerous it is to use counterfeit chargers.