If the charging indicator does not change when you plug it in, its most likely not a battery issue. In this case its likely a charging port or charging cable issue. Try a different lightening cable and charging brick (or plug it into a usb port on a computer with a different cable). If that doesn't work, try blowing out the charge port on the phone with compressed air or VERY CAREFULLY clearing it out with a toothpick. do NOT use anything metallic to do this. If its still not working after all of this, hopefully its just under a year old and you can have apple fix it under warranty.
did this work?
Please rate me if my suggestions helped. If not please let me know how I can help.