I bought a new battery for my Windows Phone, but two months later the new battery can only support my phone about 2 hours. Do you have some way to extend the usage time?
If its a genuine battery, I can recommend you to go back to dealer and get it replaced under warranty. If its not, I don't think you can do much apart from running the phone on Battery Saver mode (Always).
Check out this link and follow them if your battery is working fine now! http://www.wpcentral.com/17-tips-extend-battery-life-windows-phone
Perhaps, you should get your battery checked for genuine. If everything's ok, you can follow steps to last your battery for longer.
Turn off Hey Cortana. Turn off Data when not in use. Set your screen brightness to low. Turning battery saver on. Turning off Location and WiFi.