Why won't my battery hold a charge?

To my knowledge There are many things that can go wrong with a battery. If the phone is old and been used for a long time the electrodes in the battery don’t hold a charger. The lithium in the battery dies over time and lose its charge compasity over time. The battery could have also inflated which can happen if something short circuited in the devise or it has come in contact with water. So you may have to replace the battery or get it checked out with the company you brought the product form. Best of luck and hopefully it works