Performing a factory reset on your device might help to improve its battery life, but not necessarily. There are other things that you can do to significantly improve the battery life. You can make sure that you have the WiFi, data connection, GPS and Bluetooth deactivated at all time, if you don't use them. These services are big power consumers. Also, try reducing the brightness of the screen, don't use screen animation. All this things will help you improve the life of your battery. Also, you can use an application like DU Battery Saver. If you still have problems with the battery, even after you purchased a new one, it's possible that your device suffer a hardware malfunction that is consuming all the power and you should contact a specialized service.